What kind of drill for M16 thread

Diameter of holes for metric threads table

       The main thread pitch is highlighted in color

Metric thread, M
Tap	Drill	Tap	Drill
M1.4x0.3	1.1	M14x1.25	12.8
M1.6x0.35	1.25	M14x1	13
M2x0.4	1.6	M16x2	14
M2.5x0.45	2.05	M16x1.5	14.5
M3x0.5	2.5	M16x1.25	14.8
M3.5x0.6	2.9	M16x1	15
M4x0.7	3.3	M18x2.5	15.5
M4x0.5	3.5	M18x2	16
M5x0.8	4.2	M18x1.5	16.5
M5x0.5	4.5	M18x1	17
M6x1	5	M20x2.5	17.5
M6x0.5	5.5	M20x2	18
M7x1	6	M20x1.5	18.5
M7x0.5	6.5	M22x2.5	19.5
M8x1.25	6.8	M22x2	20
M8x1	7	M22x1.5	20.5
M8x0.75	7.2	M24x3	21
M8x0.5	7.5	M24x2	22
M9x1.25	7.8	M24x1.5	22.5
M9x1	8	M27x3	24
M10x1.5	8.5	M27x2	25
M10x1.25	8.8	M27x1.5	25.5
M10x1	9	M30x3.5	26.5
M11x1.5	9.5	M30x3	27
M11x1.25	9.8	M30x2	28
M11x1	10	M30x1.5	28.5
M12x1.75	10.2	M33x3.5	29.5
M12x1.5	10.5	M33x3	30
M12x1.25	10.8	M33x2	31
M12x1	11	M33x1.5	31.5
M14x2	12	M36x4	32
M14x1.5	12.5	M42x4.5	37.5

Pipe thread, G
Tap	Drill	Tap	Drill
G 1/8	8.8	G 1 1/4	39.5
G 1/4	11.8	G 1 3/8	42
G 3/8	15.25	G 1 1/2	45.5
G 1/2	19	G 2	57.5
G 5/8	21	G 2 1/4	63.5
G 3/4	24.5	G 2 1/2	72.5
G 7/8	28.25	G 2 3/4	78.5
G 1	30.75	G 3	85.5
G 1 1/8	35.5

Inch UNC thread
1/4x20	5.1	7/8x9	19.5
5/16x18	6.5	1x8	22.25
3/8x16	8	1 1/8x7	25
7/16x14	9.4	1 1/4x7	28.25
1/2x13	10.8	1 3/8x6	30.75
9/16x12	12.2	1 1/2x6	34
5/8x11	13.6	1 3/4x5	39.5
3/4x10	16.5	2x4	45

Inch fine thread UNF
1/4x28	5.5	3/4x16	17.5
5/16x24	6.9	7/8x14	20.5
3/8x24	8.5	1x12	23.25
7/16x20	9.9	1 1/8x12	26.5
1/2x20	11.5	1 1/4x12	29.75
9/16x18	12.9	1 3/8x12	33
5/8x18	14.5	1 1/2x12	36

Trapezoidal thread Tr
Tr 8x1.5	6.6	Tr 14x3	11.25
Tr 10x1.5	8.6	Tr 14x4	10.25
Tr 10x2	8.2	Tr 16x4	12.25
Tr 10x3	7.5	Tr 18x4	14.25
Tr 12x2	10.2	Tr 20x4	16.25
Tr 12x3	9.25	Tr 22x3	19.25
Tr 14x2	12.2	Tr 22x5	17.25

To cut internal threads with a tap, you first need to drill a hole of a certain diameter. The table shows the most popular threads and drill diameters required for drilling holes for threads.

How to find which drill bit for thread without a table?

Suppose you need to cut an M10x1.5 thread.

1. Let's find out the nominal thread diameter: 10 mm.
2. Find out the nominal thread pitch: 1.5 mm
3. Subtract the second value from the first: 10-1.5 = 8.5 mm
4. The result is 8.5 mm!

Having mastered this method, you can easily and simply select the right drill bit for cutting threads.

How to use the filter on the website to select a drill bit for threading?

For metal drills, a filter with the “For thread” parameter has been implemented, thanks to which you can find the desired drill in literally 2 mouse clicks:

1. Choosing a thread.
2. Click “Apply”.
3. We get suitable drills.

For which materials are the values ​​​​indicated in the table?

The indicated hole diameters provide cutting of metric threads in:

• gray cast iron
• carbon steels of ordinary quality
• quality structural steels
• alloyed structural steels
• high alloy steels
• corrosion-resistant, heat-resistant and heat-resistant alloys
• heat-resistant steels
• aluminum casting alloys
• copper 

A complete list of threads and diameters can be found in GOST 19257-73 - an official technical document with all the nuances and details.

Before you get started, we recommend that you read the practical tips in the article How to properly cut a thread with a tap. And there you can find suitable coolant for different materials.

Source: http://ooo-asteko.ru/diametr-otverstiy-pod-metricheskuyu-rezbu-tablitsa/

Threaded hole diameter: size table according to GOST and calculation

The strength of fastening the parts to each other is ensured by screwing the external thread carrier into the internal thread of the second product. It is important that their parameters are maintained in accordance with the standards, then such a connection will not be damaged during operation and will ensure the necessary tightness. Therefore, there are standards for the execution of carvings and its individual elements.

Threaded hole diameter

Before cutting, a hole is made inside the part for the thread, the diameter of which should not exceed its internal diameter. This is done using metal drills, the dimensions of which are given in the reference tables.

Hole parameters

The following thread parameters are distinguished:

• diameters (internal, external, etc.);
• profile shape, height and angle;
• step and entry;
• others.

The condition for connecting parts to each other is the complete coincidence of the external and internal threads. If any of them are not performed in accordance with the requirements, the fastening will be unreliable.

External thread

The fastening can be bolted or stud, which, in addition to the main parts, includes nuts and washers. Before joining, holes are formed in the parts to be fastened, and then cutting is carried out.

To perform it with maximum accuracy, you should first form a hole by drilling, equal to the size of the internal diameter, that is, formed by the tops of the protrusions.

When performing a through design, the diameter of the hole must be 5-10% larger than the size of the bolt or stud, then the following condition is met:

dresponse = (1.05..1.10)×d, (1),

where d is the nominal diameter of the bolt or stud, mm.

To determine the hole size of the second part, the calculation is carried out as follows: the pitch value (P) is subtracted from the value of the nominal diameter (d) - the resulting result is the desired value:

dresponse = d - P, (2).

The calculation results are clearly demonstrated by the table of threaded hole diameters, compiled according to GOST 19257-73, for sizes 1-1.8 mm with small and main pitches.

Nominal diameter, mm	Pitch, mm	Hole size, mm
1	0,2	0,8
1	0,25	0,75
1,1	0,2	0,9
1,1	0,25	0,85
1,2	0,2	1
1,2	0,25	0,95
1,4	0,2	1,2
1,4	0,3	1,1
1,6	0,2	1,4
1,6	0,35	1,25
1,8	0,2	1,6
1,8	0,35	1,45

An important parameter is the drilling depth, which is calculated from the sum of the following indicators:

• screw-in depth;
• reserve of external thread of the screwed-in part;
• her undercut;
• chamfers.

In this case, the last 3 parameters are for reference, and the first is calculated through the coefficients for taking into account the material of the product, which are equal for products from:

• steel, brass, bronze, titanium – 1;
• gray and ductile cast iron – 1.25;
• light alloys – 2.

Internal thread on barrel coupling

Thus, the screw-in depth is the product of the material factor and the nominal diameter, and is expressed in millimeters.

Download GOST 19257-73

Types of carving

According to the measurement system, threads are divided into metric, expressed in millimeters, and inch, measured in corresponding units. Both of these types can be made in either cylindrical or conical shapes.

Classification of threads

They can have profiles of various shapes: triangular, trapezoidal, round; divided according to application: for fasteners, plumbing elements, pipes and others.

The diameters of the preparation holes for threading depend on its type: metric, inch or pipe - this is standardized by the relevant documents.

Holes in pipe connections, expressed in inches, are specified in GOST 21348-75 for cylindrical shapes and GOST 21350-75 for conical shapes. The data is valid when using copper and nickel-free steel alloys. The cutting is carried out inside the auxiliary parts into which the pipes will be screwed - slates, clamps and others.

GOST 19257-73 shows the diameters of holes for cutting metric threads, where the tables show the size ranges of nominal diameters and pitches, as well as the parameters of holes for metric threads, taking into account the values ​​of maximum deviations.

Thread types according to GOST

The data given in the GOST 19257-73 table confirms the calculation given above, in which the parameters of holes for metric types are calculated from the nominal diameter and pitch.

GOST 6111-52 standardizes the diameters of holes for inch tapered threads. The document indicates two diameters with a taper and one without a taper, as well as drilling depths; all values, except the nominal value, are expressed in millimeters.

Adaptations

Manual or automatic cutting methods provide results in various classes of accuracy and roughness. Thus, the main tool remains a tap, which is a rod with cutting edges.

Tap device

Taps are:

• manual, for metric (M1-M68), inch – ¼-2ʺ, pipe – 1/8-2ʺ;
• machine-manual - attachments for drilling and other machines, used for the same sizes as manual ones;
• nuts, which allow you to cut a through version for thin parts, with nominal sizes of 2-33 mm.
• For cutting metric threads, use a set of rods - taps:
• rough, having an elongated intake part, consisting of 6-8 turns, and marked with one mark at the base of the shank;
• medium - with a fence of average length of 3.5-5 turns, and markings in the form of two marks;
• the finishing part has a fence of only 2-3 turns, without marks.

Tolerance control of metric thread placement

When cutting manually, if the pitch exceeds 3 mm, then use 3 taps. If the product pitch is less than 3 mm, two are enough: roughing and finishing.

Taps used for small metric threads (M1-M6) have 3 grooves that carry chips and a reinforced shank. The design of the others has 4 grooves, and the shank is through.

The diameters of all three rods for metric threads increase from rough to finish. The last threaded rod must have a diameter equal to its nominal diameter.

The taps are attached to special devices - a tool holder (if it is small) or a crank. They are used to screw the cutting rod into the hole.

Preparing holes for cutting is carried out using drills, countersinks and lathes. It is formed by drilling, and by countersinking and boring it is increased in width and improves the quality of the surface. The fixtures are used for cylindrical and conical shapes.

Thread pitch

A drill is a metal rod consisting of a cylindrical shank and a helical cutting edge. Their main geometric parameters include:

• the helical lift angle is usually 27°;
• point angle, which can be 118° or 135°.

Drills are rolled, dark blued, and shiny - ground.

Countersinks for cylindrical shapes are called counterbores. They are metal rods with two cutters twisted into a spiral and a fixed guide pin to insert the countersink into the cavity.

Cutting technique

Using a hand tap, cutting can be carried out following the following steps:

• drill an opening for a thread of the appropriate diameter and depth;
• countersink it;
• secure the tap in the holder or driver;
• align it perpendicular to the working cavity in which cutting will be carried out;
• screw the tap with light pressure clockwise into the hole prepared in advance for threading;
• Turn the tap back every half turn to cut off the chips.

Thread system

To cool and lubricate surfaces during the cutting process, it is important to use lubricants: machine oil, drying oil, kerosene and the like. Incorrectly selected lubricant can lead to poor cutting results.

Selecting drill size

The diameter of the drill for a hole for a metric thread is also determined by formula (2), taking into account its main parameters.

Drill parametersDiameter of the thread hole and its other characteristics

It is worth noting that when cutting in ductile materials, such as steel or brass, the turns increase, so it is necessary to choose a larger drill diameter for the thread than for brittle materials, such as cast iron or bronze.

In practice, drill sizes are usually slightly smaller than the required hole. Thus, Table 2 shows the ratio of the nominal and outer thread diameters, the pitch, the diameters of the hole and the drill for cutting metric threads.

Table 2. The relationship between the main parameters of metric threads with normal pitch and the diameters of the hole and drill

Nominal diameter, mm	Outer diameter, mm	Pitch, mm	Largest hole diameter, mm	Drill diameter, mm
1	0,97	0,25	0,785	0,75
2	1,94	0,4	1,679	1,60
3	2,92	0,5	2,559	2,50
4	3,91	0,7	3,422	3,30
5	4,9	0,8	4,334	4,20
6	5,88	1,0	5,153	5,00
7	6,88	1,0	6,153	6,00
8	7,87	1,25	6,912	6,80
9	8,87	1,25	7,912	7,80
10	9,95	1,5	8,676	8,50

As can be seen from the table, there is a certain dimensional limit, which is calculated taking into account thread tolerances.

The size of the drill is much smaller than the hole. So, for example, for an M6 thread, the outer diameter of which is 5.88 mm, and its largest hole value should not exceed 5.153 mm, you should use a 5 mm drill.

A hole for an M8 thread with an outer diameter of 7.87 mm will be only 6.912 mm, which means the drill for it will be 6.8 mm.

The quality of the thread depends on many factors when cutting it: from the choice of tool to the correctly calculated and prepared hole. Too little will lead to increased roughness and even breakage of the tap. Large forces applied to the tap contribute to non-compliance with tolerances and, as a result, dimensions are not maintained.

Source: https://stankiexpert.ru/tehnologii/diametr-otverstiya-pod-rezbu.html

Holes for cutting metric threads (according to GOST 19257)

Hole diameters for cutting metric threads according to GOST 9150,

GOST 24705 with tolerances according to GOST 16093 in gray cast iron according to GOST 1412,

in steels according to GOST 380, GOST 1050, GOST 4543, GOST 10702, GOST 5632 (except for nickel-based alloys),

in aluminum casting alloys according to GOST 1583,

in copper according to GOST 859.

Dimensions and maximum deviations of the diameters
of holes of threads with a large pitch

(dimensions in mm)

Nominal thread diameter d Thread pitch P Thread hole diameter with tolerance range 4H5H; 5H; 5H6H; 6H; 7H 6G; 7G 4H5H; 5H 5H6H; 6H; 6G 7H; 7G 2.5 3 3.5 4 4.5 5 6 8 10 12 14 16 18 20 22 24 27 30 33 36 39 42 45 48 52 56 60 64 68

Denomination	Deviations
0,45	2,05	2,07	+0,07	+0,09	—
0,5	2,50	2,52	+0,08	+0,19	+0,14
0,6	2,90	2,93	+0,08	+0,11	+0,15
0,7	3,30	3,33	+0,08	+0,12	+0,16
0,75	3,70	3,73	+0,09	+0,17	+0,18
0,8	4,20	4,23	+0,11	+0,19	+0,22
1	4,95	5,0	+0,17	+0,20	+0,26
1,25	6,70	6,75	+0,17	+0,20	+0,26
1,5	8,43	8,50	+0,19	+0,22	+0,30
1,75	10,20	10,25	+0,21	+0,27	+0,36
2	11,90	11,95	+0,24	+0,30	+0,40
13,90	13,95
2,5	15,35	15,40	+0,30	+0,40	+0,53
17,35	17,40
19,35	19,40
3	20,85	20,90	+0,30	+0,40	+0,53
23,85	23,90
3,5	26,30	26,35	+0,36	+0,48	+0,62
3,5	29,30	29,35
4	31,80	31,85
4	34,80	34,85	+0,36	+0,48	+0,62
4,5	37,25	37,30	+0,41	+0,55	+0,73
4,5	40,25	40,30	+0,41	+0,55	+0,73
5	42,70	42,80	+0,45	+0,60	+0,80
46,70	46,80
5,5	50,20	50,30
54,20	54,30
6	57,70	57,80
61,70	61,80

GOST provides holes for threads with large pitch d = 1.0 ÷ 2.2 mm

Dimensions and maximum deviations of the diameters of fine-pitch thread holes

Nominal thread diameter d Thread pitch P Thread hole diameter with tolerance range 4H5H; 5H; 5H6H; 6H; 7H 6G; 7G 4H5H; 5H 5H6H; 6H; 6G 7H; 7G 2.5 3 3.5 4 4.5 5 5.5 6 8 10 12 14 16 18 20 22 24 27 30 33 36 39 42 45

Denomination	Deviations
0,35	2,15	2,17	+0,05	+0,07	—
2,65	2,67
3,15	3,17
0,5	3,50	3,52	+0,08	+0,10	+0,14
4,00	4,02
4,50	4,52
5,00	5,02
0,5	5,50	5,52	+0,08	+0,10	+0,14
0,75	5,20	5,23	+0,11	+0,17	+0,22
0,5	7,50	7,52	+0,08	+0,10	+0,14
0,75	7,20	7,23	+0,11	+0,17	+0,22
1	6,95	7,00	+0,17	+0,20	+0,26
0,5	9,50	9,53	+0,08	+0,10	+0,14
0,75	9,20	9,23	+0,11	+0,17	+0,22
1	8,95	9,00	+0,17	+0,20	+0,26
1,25	8,70	8,75	+0,17	+0,20	+0,26
0,5	11,50	11,52	+0,08	+0,10	+0,14
0,75	11,20	11,23	+0,11	+0,17	+0,22
1	10,99	11,00	+0,17	+0,17	+0,26
1,25	10,70	10,75	+0,17	+0,20	+0,26
1,5	10,43	10,50	+0,19	+0,22	+0,30
0,5	13,50	13,52	+0,08	+0,10	+0,14
0,75	13,20	13,23	+0,11	+0,17	+0,22
1	12,95	13,00	+0,17	+0,20	+0,26
1,25	12,70	12,75	+0,17	+0,20	+0,26
1,5	12,43	12,50	+0,19	+0,22	+0,30
0,5	15,50	15,52	+0,08	+0,10	+0,14
0,75	15,20	15,23	+0,11	+0,17	+0,22
1	14,95	15,00	+0,17	+0,20	+0,26
1,5	14,43	14,50	+0,19	+0,22	+0,30
0,5	17,50	17,52	+0,08	+0,10	+0,14
0,75	17,20	17,23	+0,11	+0,17	+0,22
1	16,95	17,00	+0,17	+0,20	+0,26
1,25	16,43	16,50	+0,19	+0,22	+0,30
1,5	15,90	15,95	+0,24	+0,30	+0,40
0,5	19,50	19,52	+0,08	+0,10	+0,14
0,75	19,20	19,23	+0,11	+0,17	+0,22
1	18,95	19,00	+0,17	+0,20	+0,26
1,5	18,43	18,50	+0,19	+0,22	+0,30
2	17,90	17,95	+0,24	+0,30	+0,40
0,5	21,50	21,52	+0,08	+0,10	+0,14
0,75	21,20	21,23	+0,11	+0,17	+0,22
1	20,95	21,00	+0,17	+0,20	+0,26
1,5	20,43	20,50	+0,19	+0,22	+0,30
2	19,90	19,95	+0,24	+0,30	+0,40
0,75	23,20	23,23	+0,11	+0,17	+0,22
1	22,95	23,00	+0,17	+0,20	+0,26
1,5	22,43	22,50	+0,19	+0,22	+0,30
2	21,90	21,95	+0,24	+0,30	+0,40
0,75	26,20	26,23	+0,11	+0,17	+0,22
1	25,95	26,00	+0,17	+0,20	+0,26
1,5	25,43	25,50	+0,19	+0,22	+0,30
2	24,90	24,95	+0,24	+0,30	+0,40
0,75	29,20	29,23	+0,11	+0,17	+0,22
1	28,95	29,00	+0,17	+0,20	+0,26
1,5	28,43	28,50	+0,19	+0,22	+0,30
2	27,90	27,95	+0,24	+0,30	+0,40
3	26,85	26,90	+0,30	+0,40	+0,53
0,75	32,20	32,23	+0,11	+0,17	+0,22
1	31,95	32,00	+0,17	+0,20	+0,26
1,5	31,43	31,50	+0,19	+0,22	+0,30
2	30,90	30,95	+0,24	+0,30	+0,40
3	29,85	29,90	+0,30	+0,40	+0,53
1	34,95	35,00	+0,17	+0,20	+0,26
1,5	34,43	34,50	+0,19	+0,22	+0,30
2	33,90	33,95	+0,24	+0,30	+0,40
3	32,85	32,90	+0,30	+0,40	+0,53
1	37,95	38,00	+0,17	+0,20	+0,26
1,5	37,43	37,50	+0,19	+0,22	+0,30
2	36,90	36,95	+0,24	+0,30	+0,40
3	35,85	35,90	+0,30	+0,40	+0,53
1	40,95	41,00	+0,17	+0,20	+0,26
1,5	40,43	40,50	+0,19	+0,22	+0,30
2	39,90	39,95	+0,24	+0,30	+0,40
3	38,85	38,90	+0,30	+0,40	+0,53
4	37,80	37,85	+0,36	+0,48	+0,62
1	43,95	44,00	+0,17	+0,20	+0,26
1,5	43,43	43,50	+0,19	+0,22	+0,30
2	42,90	42,95	+0,24	+0,30	+0,40
3	41,85	41,90	+0,30	+0,40	+0,53
4	40,80	40,85	+0,36	+0,48	+0,62

GOST provides holes for threads with d = 1.0 ÷ 200 mm and for the 3rd row.

GOST provides a method for determining the diameters of holes for cutting metric threads for materials of high viscosity.

See also:

Source: http://razvitie-pu.ru/?page_id=4502

Drill and tap hole size charts: metric, inch

Making internal threads is usually not difficult. But there are some features of using the tool and selecting holes for cutting metric threads.

Types of thread

internal thread on the barrel coupling

They differ in their main characteristics:

• diameter calculation system (inch, metric, others);
• number of passes (two-, three- or single-pass);
• profile shape (rectangular, trapezoidal, triangular, round);
• direction of rotation of the screw (left or right);
• placement on the part (internal or external);
• shape of the part (cone or cylinder);
• purpose (running, fastening and sealing or fastening).

According to the listed characteristics, the following types are distinguished:

• cylindrical (MJ);
• metric and conical (M, MK);
• pipe (G, R);
• Edison round (E);
• trapezoidal (Tr);
• round for plumbing fasteners (Kp);
• persistent (S, S45);
• inch, including cylindrical and conical (BSW, UTS, NPT);
• oil range.

Tools for internal threading

To make internal cutting, you need a tap - a screw-shaped tool with sharp grooves. The rod can be shaped like a cone or a cylinder. The grooves run lengthwise and break the thread into sections called combs. It is the edges of the combs that are the working surfaces.

To ensure a clean groove, the metal is removed gradually, in layers. This requires one very long tool or set.

Single taps are also found on sale; they are often used to correct broken threads. To cut a new one, buy a kit. Therefore, taps are usually sold in pairs: for roughing and for finishing work.

The first one cuts a shallow groove, the second one cleans and deepens it. There are also three-pass tools. Thin taps, up to 3 millimeters, are sold in twos, wider ones - in threes. Three-pass taps are inserted into the gates.

The design of the knobs is different, but their size must match the size of the cutter.

The tools in the set are distinguished by the marks marked on the tail end. If you look closely, you will notice differences in shape:

• the first tap has heavily cut tooth tips, the outer diameter is slightly smaller than the other tools in the set;
• second tap with shorter fence segment, longer ridges. Its diameter is slightly larger than that of the first;
• the third tap has full ridges of teeth, and its diameter should match the dimensions of the future thread.

Taps are divided into pipe taps (marked “G”) for cutting threads inside the pipe, and metric taps, which are more common.

The quality directly depends on the properties of the tap: it must be made of good metal and sharp. To extend the life of the tool and improve the quality of the thread, lubricant is used. Usually, to acquire a stable cutting skill, you need to make 3 - 5 attempts.

Cutting process

diameters of thread holes depending on the type of metal

Before you start cutting, you should use drills to make a hole in the workpiece. The diameter of the drill hole must match the internal thread size. When the size of the hole made with drills is chosen incorrectly, the tool can break or the grooves will turn out to be of poor quality.

During cutting, part of the metal does not fall out with chips, but is pressed along the working surfaces of the tap, forming a groove profile on the workpiece. Taking this feature into account, the size of the drill used to make the hole for the thread is selected slightly smaller than the nominal diameter of the future thread.

For example, when cutting M5 (groove diameter is 5 mm), you should choose a drill for a 4.2 mm hole. To cut M4, the diameter of the drill must be 3.3 millimeters, and before working with an M6 tap, a hole is first made with a 5 mm drill. This indicator is calculated taking into account the thread pitch.

The pitch can be calculated mathematically, but in practice they resort to correspondence tables, where for an M5 tap the pitch is 0.8, for M4 this figure is 0.7, for M6 - 1. We subtract the pitch index from the diameter and get the required diameter of the drill.

When working with brittle metals, such as cast iron, the drill diameter should be reduced by 0.1 mm compared to the size recommended in the table.

The formula for calculating the hole diameter when working with three-pass taps:

Up=Dm * 0.8;

here: Dm is the diameter of the tap.

Type	Diameter	Step
M1	0,75	0,25
M1,2	0,95	0,25
1,4	1,1	0,3
1,7	1,3	0,36
2,6	1,6	0,4
2,8	1,9	0,4
M3	2,1	0,46
M3	2,5	0,5
M4	3,3	0,7
M5	4,1	0,8
M6	4,9	1
M8	6,7	1,25
M10	8,4	1,5

Table 1. Correspondence between thread diameters and preparation hole

Before starting work, the tap is inserted into a square shank - a knob. The collars can be regular or ratchet. The carving is done carefully, the first pass is made with a No. 1 tap to the end. Particular attention must be paid to the direction of movement: only clockwise, and some effort must be applied. It is done like this: 1/2 turns along the stroke alternate with 1/4 turns against the screw stroke to destroy the chips.

Thread in inches	External D, mm	Diameter, mm	Pitch, mm
1\8″	2,095	0,74	1,058
1\4″	6,35	4,72	1,27
3\16″	4,762	3,47	1,058
5\16″	7,938	6,13	1,411
7\16″	11,112	8,79	1,814
3\8″	9,525	7,49	1,588

Table 2. Hole diameters for inch threads

A couple drops of lubricant will make working on blind threaded holes much easier. Although machine oil is sometimes used as a lubricant, drying oil is optimal for working with steel. With aluminum alloys, it is preferable to use kerosene, alcohol or turpentine. Technical oil can also be used, but with less effect.

Homemade tap for aluminum alloys

To create internal threads in brass or light alloy parts, you can use homemade tools and drills from a regular set. Calibrated steel wire will do. Using a die, an external thread is cut on it, after which the workpiece is hardened. After hardening, it is necessary to release the part to the color of ripe straw. The cutting edges are sharpened using a whetstone or sharpener, after first clamping the part into a collet chuck.

about how internal threads are cut:

Complete GOST for hole diameters for cutting metric threads

Source: http://StanokGid.ru/osnastka/diametr-otverstij-pod-rezbu.html

Diameter of threaded drill (table)

SVERLA.info » Articles » Threaded drill diameter

       The main thread pitch is highlighted in color

Metric thread, M
Tap	Drill	Tap	Drill
M1.4x0.3	1.1	M14x1.25	12.8
M1.6x0.35	1.25	M14x1	13
M2x0.4	1.6	M16x2	14
M2.5x0.45	2.05	M16x1.5	14.5
M3x0.5	2.5	M16x1.25	14.8
M3.5x0.6	2.9	M16x1	15
M4x0.7	3.3	M18x2.5	15.5
M4x0.5	3.5	M18x2	16
M5x0.8	4.2	M18x1.5	16.5
M5x0.5	4.5	M18x1	17
M6x1	5	M20x2.5	17.5
M6x0.5	5.5	M20x2	18
M7x1	6	M20x1.5	18.5
M7x0.5	6.5	M22x2.5	19.5
M8x1.25	6.8	M22x2	20
M8x1	7	M22x1.5	20.5
M8x0.75	7.2	M24x3	21
M8x0.5	7.5	M24x2	22
M9x1.25	7.8	M24x1.5	22.5
M9x1	8	M27x3	24
M10x1.5	8.5	M27x2	25
M10x1.25	8.8	M27x1.5	25.5
M10x1	9	M30x3.5	26.5
M11x1.5	9.5	M30x3	27
M11x1.25	9.8	M30x2	28
M11x1	10	M30x1.5	28.5
M12x1.75	10.2	M33x3.5	29.5
M12x1.5	10.5	M33x3	30
M12x1.25	10.8	M33x2	31
M12x1	11	M33x1.5	31.5
M14x2	12	M36x4	32
M14x1.5	12.5	M42x4.5	37.5

Pipe thread, G
Tap	Drill	Tap	Drill
G 1/8	8.8	G 1 1/4	39.5
G 1/4	11.8	G 1 3/8	42
G 3/8	15.25	G 1 1/2	45.5
G 1/2	19	G 2	57.5
G 5/8	21	G 2 1/4	63.5
G 3/4	24.5	G 2 1/2	72.5
G 7/8	28.25	G 2 3/4	78.5
G 1	30.75	G 3	85.5
G 1 1/8	35.5

Inch UNC thread
1/4x20	5.1	7/8x9	19.5
5/16x18	6.5	1x8	22.25
3/8x16	8	1 1/8x7	25
7/16x14	9.4	1 1/4x7	28.25
1/2x13	10.8	1 3/8x6	30.75
9/16x12	12.2	1 1/2x6	34
5/8x11	13.6	1 3/4x5	39.5
3/4x10	16.5	2x4	45

Inch fine thread UNF
1/4x28	5.5	3/4x16	17.5
5/16x24	6.9	7/8x14	20.5
3/8x24	8.5	1x12	23.25
7/16x20	9.9	1 1/8x12	26.5
1/2x20	11.5	1 1/4x12	29.75
9/16x18	12.9	1 3/8x12	33
5/8x18	14.5	1 1/2x12	36

Trapezoidal thread Tr
Tr 8x1.5	6.6	Tr 14x3	11.25
Tr 10x1.5	8.6	Tr 14x4	10.25
Tr 10x2	8.2	Tr 16x4	12.25
Tr 10x3	7.5	Tr 18x4	14.25
Tr 12x2	10.2	Tr 20x4	16.25
Tr 12x3	9.25	Tr 22x3	19.25
Tr 14x2	12.2	Tr 22x5	17.25

To cut internal threads with a tap, you first need to drill a hole of a certain diameter. The table shows the most popular threads and drill diameters required for drilling holes for threads.

Hole diameter for metric thread: size table according to GOST

Despite the fact that cutting internal threads is not a complex technological operation, there are some features of preparation for this procedure. Thus, it is necessary to accurately determine the dimensions of the preparation hole for threading, and also select the right tool, for which special tables of drill diameters for threads are used. For each type of thread, it is necessary to use the appropriate tool and calculate the diameter of the preparation hole.

The thread diameter and through hole must comply with the standards, otherwise the grooves will come out too small and the threaded connection will be unreliable

Types and parameters of thread

The parameters by which threads are divided into different types are:

• units of diameter (metric, inch, etc.);
• number of thread starts (one-, two- or three-thread);
• the shape in which the profile elements are made (triangular, rectangular, round, trapezoidal);
• direction of rise of turns (right or left);
• location on the product (external or internal);
• surface shape (cylindrical or conical);
• purpose (fastening, fastening and sealing, chassis).

Metric thread parameters

Depending on the above parameters, the following types of thread are distinguished:

• cylindrical, which is designated by the letters MJ;
• metric and conical, designated M and MK respectively;
• pipe, designated by the letters G and R;
• with a round profile, named after Edison and marked with the letter E;
• trapezoidal, designated Tr;
• round, used for installation of sanitary fittings, – Kr;
• thrust and thrust reinforced, marked as S and S45, respectively;
• inch thread, which can also be cylindrical and conical - BSW, UTS, NPT;
• used to connect pipes installed in oil wells.

Application of the tap

Before you start threading, you need to determine the diameter of the preparation hole and drill it. To facilitate this task, a corresponding GOST was developed, which contains tables that allow you to accurately determine the diameter of the threaded hole. This information makes it easy to select the drill size.

To cut metric threads on the inner walls of a hole made with a drill, a tap is used - a screw-shaped tool with cutting grooves, made in the form of a rod, which can have a cylindrical or conical shape. On its side surface there are special grooves located along its axis and dividing the working part into separate segments, which are called combs. The sharp edges of the combs are precisely the working surfaces of the tap.

Tap: design and parameters

In order for the turns of the internal thread to be clean and neat, and for its geometric parameters to correspond to the required values, it must be cut gradually, by gradually removing thin layers of metal from the surface being treated.

That is why for this purpose they use either taps, the working part of which is divided along the length into sections with different geometric parameters, or sets of such tools.

Single taps, the working part of which has the same geometric parameters along its entire length, are needed in cases where it is necessary to restore the parameters of an existing thread.

The minimum set with which you can sufficiently perform machining of threaded holes is a set consisting of two taps - rough and finishing. The first one cuts a thin layer of metal from the walls of the hole for cutting metric threads and forms a shallow groove on them, the second one not only deepens the formed groove, but also cleans it.

Types of thread taps and their differences

Minimum set of taps

Combination two-pass taps or sets consisting of two tools are used for tapping small diameter holes (up to 3 mm). To machine holes for larger metric threads, you must use a combination three-pass tool or a set of three taps.

To manipulate the tap, a special device is used - a wrench. The main parameter of such devices, which can have different designs, is the size of the mounting hole, which must exactly match the size of the tool shank.

Some types of tap drivers

When using a set of three taps that differ both in their design and geometric parameters, the sequence of their use must be strictly observed. They can be distinguished from each other both by special marks applied to the shanks and by design features.

1. The tap, with which the hole for cutting metric threads is processed first, has the smallest diameter among all the tools in the set and cutting teeth, the upper part of which is heavily cut off.
2. The second tap has a shorter fence and longer combs. Its working diameter is intermediate between the diameters of the other tools in the set.
3. The third tap, with which the hole for cutting metric threads is processed last, is characterized by full ridges of cutting teeth and a diameter that must exactly match the size of the thread being formed.

Set of three taps

https://www.youtube.com/watch?v=u-adRBIR6Ys

Taps are used primarily for cutting metric threads. Much less often than metric ones, taps designed for processing the internal walls of pipes are used. In accordance with their purpose, they are called pipe, and they can be distinguished by the letter G present in their markings.

Internal thread cutting technology

As mentioned above, before starting work, you need to drill a hole, the diameter of which must exactly fit a thread of a certain size. It should be borne in mind: if the diameters of the holes intended for cutting metric threads are chosen incorrectly, this can lead not only to poor quality execution, but also to breakage of the tap.

Considering the fact that the tap, when forming threaded grooves, not only cuts the metal, but also pushes it, the diameter of the drill for making threads should be slightly smaller than its nominal diameter. For example, a drill for making M3 threads should have a diameter of 2.5 mm, for M4 - 3.3 mm, for M5 you should choose a drill with a diameter of 4.2 mm, for M6 threads - 5 mm, M8 - 6.7 mm, M10 - 8.5 mm, and for M12 - 10.2.

Table 1. Main diameters of holes for metric threads

Table 2. Diameters of holes for inch threads

All diameters of drills for GOST threads are given in special tables. Such tables indicate the diameters of drills for making threads with both standard and reduced pitches, but it should be borne in mind that holes of different diameters are drilled for these purposes. In addition, if threads are cut in products made of brittle metals (such as cast iron), the diameter of the thread drill obtained from the table must be reduced by one tenth of a millimeter.

You can familiarize yourself with the provisions of GOST regulating the cutting of metric threads by downloading the document in pdf format from the link below.
GOST 19257-73 Holes for cutting metric threads. Diameters Download

The diameters of drills for metric threads can be calculated independently. From the diameter of the thread that needs to be cut, it is necessary to subtract the value of its pitch.

The thread pitch itself, the size of which is used when performing such calculations, can be found out from special correspondence tables.

In order to determine what diameter the hole needs to be made using a drill if a three-start tap is used for threading, you must use the following formula:

To = Dm x 0.8, where:

Do is the diameter of the hole that must be made using a drill,

Dm is the diameter of the tap that will be used to process the drilled element.

Scheme of cutting internal threads with a tap

The drivers into which the threaded tap is inserted can have a simple design or be equipped with a ratchet. You should work with such devices with tools fixed in them very carefully. To obtain high-quality and clean threads, rotating the tap clockwise, performed half a turn, must be alternated with turning it one-fourth of a turn against the thread.

The thread will be cut much easier if you use a lubricant during this procedure. The role of such a lubricant when cutting threads in steel products can be played by drying oil, and when processing aluminum alloys - alcohol, turpentine or kerosene. If such technical fluids are not at hand, then ordinary machine oil can be used to lubricate the tap and the thread being cut (however, it has less effect than the substances listed above).

Source: http://met-all.org/obrabotka/prochie/diametr-sverla-pod-rezbu-metricheskuyu-tablitsa-razmerov.html

What hole diameter should I drill for metric threads? — Homo habilis. Magazine for skilled people

Yuri Makarov Category: Workshop: March 30, 2014 56205

:  5 / 5

Sam Schmidt, flickr.com CC BY

Threaded connections are one of the most common types of detachable connections. But if fasteners with external threads (screws, studs) are most often purchased ready-made, then the internal threads have to be cut by the craftsman himself when manufacturing the part. To do this, a hole with a certain diameter is drilled into the part.

The diameter of the hole for the internal thread depends on the nominal diameter of the thread and the pitch of the thread. This is usually indicated on the drawing as M8x1. The letter “M” denotes a metric thread, the number after the letter is the nominal diameter, the number after the sign “x” is the thread pitch. If a step is not specified, then the main (major) step is assumed. The main thread pitch is preferred and is specified by the standard for each size.

For each combination of diameter and thread pitch, there is an optimal hole diameter. The easiest way to determine this diameter is from the table, which shows the most common sizes that a home craftsman may encounter. in bold in the table. The table is applicable for steels, cast irons, aluminum and its alloys, and copper.

Thread	Thread pitch	Nominal hole diameter (maximum)
M2	0,25	1,75–1,77 (1,81)
0,4	1,60–1,62 (1,68)
M2.5	0,35	2,15–2,17 (2,22)
0,45	2,05–2,07 (2,13)
M3	0,35	2,65–2,67 (2,72)
0,5	2,50–2,52 (2,58)
M4	0,5	3,50–3,52 (3,64)
0,7	3,30–3,33 (3,46)
M5	0,5	4,50–4,52 (4,64)
0,8	4,2–4,23 (4,42)
M6	0,5	5,50–5,52 (5,64)
0,75	5,20–5,23 (5,42)
1,0	4,95–5,00 (5,21)
M7	0,5	6,50–6,52 (6,64)
0,75	6,20–6,23 (6,42)
1,0	5,95–6,00 (6,26)
M8	0,5	7,50–7,52 (7,64)
0,75	7,20–7,23 (7,42)
1	6,95–7,00 (7,21)
1,25	6,70–6,75 (6,96)
M9	0,5	8,50–8,52 (8,64)
0,75	8,20–8,23 (8,42)
1	7,95–8,00 (8,21)
1,25	7,70–7,75 (7,96)
M10	0,5	9,50–9,52 (9,64)
0,75	9,20–9,23 (9,42)
1	8,95–9,00 (9,21)
1,25	8,70–8,75 (8,96)
1,5	8,43–8,50 (8,73)
M11	0,5	10,50-10–52 (10,64)
0,75	10,20–10,23 (10,42)
1	9,95–10,00 (10,21)
1,5	9,43–9,50 (9,73)
M12	0,5	11,50–11,52 (11,64)
0,75	11,20–11,23 (11,42)
1	10,95–11,00 (11,21)
1,25	10,70–10,75 (10,96)
1,5	10,43–10,50 (10,73)
1,75	10,20–10,25 (10,56)
M14	0,5	13,50–13,52 (13,64)
0,75	13,20–13,23 (13,42)
1	12,95–13,00 (13,21)
1,25	12,70–12,75 (12,96)
1,5	12,43–12,50 (12,73)
2	11,90–11,95 (12,30)
M16	0,5	15,50–15,52 (15,64)
0,75	15,20–15,23 (15,42)
1	14,95–15,00 (15,26)
1,5	14,43–14,50 (14,73)
2	13,90–13,95 (14,30)
M18	0,5	17,50–17,52 (17,64)
0,75	17,20–17,23 (17,42)
1	16,95–17,00 (17,21)
1,5	16,43–16,50 (16,73)
2	15,90–15,95 (16,30)
2,5	15,35–15,40 (15,88)
M20	0,5	19,50–19,52 (19,64)
0,75	19,20–19,23 (19,42)
1	18,95–19,00 (19,21)
1,5	18,43–18,50 (18,73)
2	17,90–17,95 (18,3)
2,5	17,35–17,40 (17,88)

Reducing the hole diameter makes threading more difficult and can cause the tap to break , especially in hard materials. Increasing the hole diameter will not allow cutting the full profile; the thread will be weakened.

The drill for drilling holes is selected from the available set as close as possible to the recommended diameter, or, in extreme cases, to the limit. It should be borne in mind that when drilling holes with a hand drill, the hole will inevitably break, so it is better to take a drill closer to the minimum recommended diameter. It is convenient to use sets that contain drills specifically for holes for metric threads.

In most cases, a home craftsman rarely produces critical, highly loaded parts, so sometimes it is possible to allow a slight increase in the diameter of the hole relative to the maximum size.

If the part performs purely decorative functions, does not experience heavy loads and under no circumstances can create a danger to humans, the margin for threads can be up to 1/3 - 1/5 of a pitch or even less. For example, for a M10x1.5 thread, you can increase the hole to 9.5-9.7 mm. In this case, the screw or pin must fit into the part by at least 8-10 full threads.

We recommend reading

Source: https://homo-habilis.ru/masterskaya/231-kakoj-diametr-otverstiya-sverlit-pod-metricheskuyu-rezbu

Threaded hole: diameter, classification of types, size table - Machine

18.12.2019

The strength of fastening the parts to each other is ensured by screwing the external thread carrier into the internal thread of the second product. It is important that their parameters are maintained in accordance with the standards, then such a connection will not be damaged during operation and will ensure the necessary tightness. Therefore, there are standards for the execution of carvings and its individual elements.

Threaded hole diameter

Before cutting, a hole is made inside the part for the thread, the diameter of which should not exceed its internal diameter. This is done using metal drills, the dimensions of which are given in the reference tables.