Choosing the right tap drill size to achieve the optimum size of thread taps is crucial. However, it’s not as easy as it seems. Usually, it’s considered a major problem for many design manufacturers and thus end up having stripped threads and weak connections. Do you get frustrated by getting it wrong, or by having bad threads? Then don’t worry, there’s a simple solution.

In determining the right tap drill size, it is necessary to consider the tapped hole type and intended material. In the majority of the thread forms, the tap drill should produce a hole; a depth of 75% of the thread. Since it’s important to mitigate reconnecting issues between the two components over and over again. Printed circuit boards (PCBs) may use fine or coarse threads and normally need modifications over time.

So, after a basic understanding, let’s take a look deeper at the different types of threads you can use for different nominal sizes.

What Is a Tap Drill?

A tap drill makes a hole designed to take a particular thread during tapping. The hole diameter is far as important as the thread engagement degree because the overall formation of the connection is concerned. Moreover, the tap drill size is often undersized of the full thread diameter.

So, the tap can cut the threads into the material. In most routine threading processes, the tap drill size is selected to be about 75% of the thread depth for adequate thread formation and strength. In addition, the correct tap drill size depends on the type of thread and the material being tapped—whether coarse, fine, or metric.

Why It’s Important To Keep Correct Tap Drill Size?

Here are the key benefits of ensuring accurate tapping:

Optimum Thread Engagement

A correct tap drill size enables the tap to thread deeper enough to provide a firm hold to connected parts. This makes it possible for the threads to interact well with the fastener and leads to strong joints. Additionally, a well-specified hole increases the load-bearing capabilities of the threaded connection to higher-limit loads.

Prevents Stripped Threads

An oversized hole can result in threads that do not engage correctly. If the hole diameter is too large, the threads may not have enough material to engage resulting in poor fastening. In addition, when you select the correct size of the tap drill, you can be in a position to get a better and more effective hold.

Minimizes Tool Wear and Breakage

Employing the wrong size of drill increases pressure on the tap and the drill bit. Thus, can also increase wear and tear. If you use a correctly sized tap drill, the tools slice through the material with minimum resistance. So, there’s less chance of the tool breaking or chipping.

Optimizes Tapping Efficiency

If the hole made is the same size as the tap size, the tap can be cut perfectly and in an even manner to avoid binding and seizing. In addition, the right size reduces the force required to tap the hole to complete the process in a shorter turnaround.

Promotes Thread Accuracy

The right hole size is moreover, significant for accurate threads to be formed. When using a specific tap drill you can ensure the thread line will be made correct. Thus, you can minimize misalignments and uneven pressure circumstances of failures.

How to Calculate Tap Drill Size

To calculate the correct tap drill size, use the following formula:

Tap Drill Size = Major Diameter – Thread Pitch

• Major Diameter: Outer diameter of the threaded fastener (bolt or screw).
• Thread Pitch: It defines the distance between threads (for metric threads, It is the pitch; for imperial threads, it’s the number of threads/inch).

For example:

For a M10 x 1.5 (metric) thread:

Major Diameter = 10 mm

Thread Pitch = 1.5 mm

Tap Drill Size = 10 mm – 1.5 mm = 8.5 mm

For a 1/4″-20 (imperial) thread:

Major Diameter = 0.250″ (1/4 inch)

Thread Pitch = 1/20″ (0.050″)

Tap Drill Size = 0.250″ – 0.050″ = 0.200″

The formula above provides the ideal hole size to achieve the correct thread size, engagement, and strength.

Common Tap Sizes and Corresponding Drill Bit Sizes

The table gives you the corresponding drill sizes for both Coarse and Fine thread types across various standard thread sizes.

Thread Size	Coarse Thread Drill Size	Fine Thread Drill Size
1-64	.0595 (No. 53)	.0469 (3/64)
2-56	.0700 (No. 50)	.0595 (No. 53)
3-48	.0785 (No. 47)	.0700 (No. 50)
4-40	.0890 (No. 43)	.0820 (No. 45)
5-40	.1015 (No. 38)	.0935 (No. 42)
6-32	.1065 (No. 36)	.1040 (No. 37)
8-32	.1360 (No. 29)	.1130 (No. 33)
10-24	.1495 (No. 25)	.1360 (No. 29)
12-24	.1770 (No. 16)	.1590 (No. 21)
1/4-20	.2010 (No. 7)	.1820 (No. 14)
5/16-18	.2570 (‘F’)	.2130 (No. 3)
3/8-16	.3125 (5/16)	.2720 (‘I’)
7/16-14	.3680 (‘U’)	.3320 (‘Q’)
1/2-13	.4219 (27/64)	.3906 (25/64)
9/16-12	.4844 (31/64)	.4531 (29/64)
5/8-11	.5312 (17/32)	.5156 (33/64)
3/4-10	.6562 (21/32)	.5781 (37/64)
7/8-9	.7656 (49/64)	.6875 (11/16)
1″-8	.8750 (7/8)	.8125 (13/16)
		.9375 (59/64)

Different Types of Threads

The most common types of threads include

Metric or International Threads

Metric (International) Threads are global thread classes. These threads are currently described by ISO (International Organization for Standardization). They are generally specified by two key dimensions:

• Pitch: The amount of space between the threads (measured in millimeters).
• Major Diameter: The number of threads per unit length in inches; it is the outer diameter of the threaded fastener in millimeters.

Some common metric thread series include; ISO Metric (M), for instance M6, M8, M10, where “M” stands for metric and the figure for the major diameter. For example, M10 x 1.5 means a 10 mm diameter of the thread major and a 1.5 mm diameter of thread pitch respectively.

Standard Metric Thread Tap Drill Size Chart

Thread Size	Major Diameter (mm)	Pitch (mm)	Tap Drill Size (mm)
M3	3.0	0.5	2.5
M4	4.0	0.7	3.3
M5	5.0	0.8	4.2
M6	6.0	1.0	5.0
M8	8.0	1.25	6.8
M10	10.0	1.5	8.5
M12	12.0	1.75	10.2
M14	14.0	2.0	11.8
M16	16.0	2.0	13.0
M18	18.0	2.5	15.0
M20	20.0	2.5	16.5
M22	22.0	2.5	18.5
M24	24.0	3.0	19.5
M27	27.0	3.0	22.0
M30	30.0	3.5	24.5
M33	33.0	3.5	26.5

Right-Hand Threads

In the right-hand thread, the fastener screws in clockwise and unscrew when anti-clockwise. Design engineers normally use these as ordinary screws, bolts, and nuts, unless they are specially designed for a particular use.

Furthermore, right-hand threads are directionally standardized to fit all applications and easily integrate with both manual and automatic operations.

Right-Hand Thread Tap Drill Size Chart

Thread Size	Major Diameter (inches)	Pitch (inches)	Tap Drill Size (inches)
1/4-20	0.2500	0.0500	0.2010
5/16-18	0.3125	0.0550	0.2570
3/8-16	0.3750	0.0625	0.3125
7/16-14	0.4375	0.0714	0.3680
1/2-13	0.5000	0.0769	0.4219
9/16-12	0.5625	0.0833	0.4844
5/8-11	0.6250	0.0909	0.5312
3/4-10	0.7500	0.1000	0.6562
7/8-9	0.8750	0.1111	0.7656
1″-8	1.0000	0.1250	0.8750

Left Hand Threads

Left-hand(LH) threads are used for reverse turning moments. These are tightened by a clockwise turn of a fastener and loosened by an anti-clockwise turn. The rotation applied to the bolt can loosen a normal right-hand thread in these situations. The common uses of left-hand threads include: rotating machinery, automobile wheel nuts, some valve fittings, and bicycles that need reverse rotation to undo.

Left-Hand Thread Dimensions and Tolerance Table — Inch

Thread Size	Shoulder Diameter (Min. to Max)	Head Diameter	Head Height	Drive Size	Head Appearance
1/8	.121 to .123	1/4	1/8	5/64	Knurl Only (Screws produced before 2/1/2021 may have finger grip AMPG Mark only)
5/32	.152 to .154	9/32	1/8	3/32	Head Mark and Knurl
3/16	.183 to .185	5/16	5/32	3/32	Head Mark and Knurl
1/4	.246 to .248	3/8	3/16	1/8	Head Mark and Knurl
5/16	.308 to .310	7/16	7/32	5/32	Head Mark and Knurl
3/8	.371 to .373	9/16	1/4	3/16	Head Mark and Knurl
1/2	.496 to .498	3/4	5/16	1/4	Head Mark and Knurl

Taper Threads

Taper Threads entail a tapering form or conical threads typically reduce in size. They form very compact and water-tight seals when tightened.

 

These threads are usually applied in NPT (National Pipe Tapered) threads. It creates an interlocking seal that prevents the passage of pressure. Moreover, taper threads are employed in plumbing, hydraulic, and pneumatic applications. Correct torque will guarantee that the seal is tight without any damage.

Tapered Pipe Threads (NPT) Dimensions and Engagement for Standard Sizes

Nominal Size	Outside Diameter (D)	Threads per Inch (n)	Pitch of Thread (P)	Pitch Dia at the Beginning of External Thread (E0)	Hand tight Engagement Length L1	Diameter E1	Hand tight Engagement Length L2	Diameter E2
1/16	0.3125	27	0.0370	0.27118	0.160	0.28118	0.2611	0.28750
1/8	0.405	27	0.0370	0.36351	0.1615	0.37360	0.2639	0.38000
1/4	0.540	18	0.0555	0.47739	0.2278	0.49163	0.4018	0.50250
3/8	0.675	18	0.0555	0.61201	0.240	0.62701	0.4078	0.63750
1/2	0.840	14	0.0714	0.75843	0.320	0.77843	0.5337	0.79179
3/4	1.050	14	0.0714	0.96768	0.339	0.98887	0.5457	1.00179
1	1.315	11.5	0.0869	1.21363	0.400	1.23863	0.6828	1.25630
1-1/4	1.660	11.5	0.0869	1.55713	0.420	1.58338	0.7068	1.60130
1-1/2	1.900	11.5	0.0869	1.79609	0.420	1.82234	0.7235	1.84130
2	2.375	11.5	0.0869	2.26902	0.436	2.29627	0.7565	2.31630
2-1/2	2.875	8	0.1250	2.71953	0.682	2.76216	1.1375	2.79062
3	3.5	8	0.1250	3.34062	0.766	3.38850	1.2000	3.41562
3-1/2	4.0	8	0.1250	3.83750	0.821	3.88881	1.2500	3.91562
4	4.5	8	0.1250	4.33438	0.844	4.38712	1.3000	4.41562
5	5.563	8	0.1250	5.39073	0.937	5.44929	1.4063	5.47862
6	6.625	8	0.1250	6.44609	0.958	6.50597	1.5125	6.54062
8	8.625	8	0.1250	8.43359	1.063	8.50003	1.7125	8.54062
10	10.750	8	0.1250	10.54531	1.210	10.62094	1.9250	10.66562
12	12.750	8	0.1250	12.53281	1.360	12.61781	2.1250	12.66562

V-Shaped Threads

V-shaped threads keep an angled cross-sectional shape with angles from 30 to 60 degrees.

These threads are designed by engineers to offer appreciable mechanical interconnects. In addition to their application, they are mainly used in bolts, screws, and other fasteners. Their shape enables the load to be spread evenly along the entire length of the thread, and across the width as well. High torque is best served with V-shaped threads.

British Standard Threads

British Standard Threads (BST) is a group of thread forms mainly used in Britain and other countries of the Commonwealth.

BSW threads are of 55° thread angle. In addition, BSF threads confine finer pitches for use in more accurate purposes. Industries like machinery, automotive, and engineering use these threads for secure joining purposes.

G/BSP Thread Type – British Standard Pipe (BSPT)

Dash Size (Nominal Size)	Thread Pitch	Male Thread O.D. (mm)	Male Thread O.D. (inches)	Female Thread I.D. (mm)	Female Thread I.D. (inches)
-02 (1/8)	28	9.7	0.38	8.9	0.35
-04 (1/4)	19	13.2	0.52	11.9	0.47
-06 (3/8)	19	16.5	0.65	15.2	0.60
-08 (1/2)	14	20.8	0.82	19.1	0.75
-10 (5/8)	14	22.4	0.88	20.3	0.80
-12 (3/4)	14	26.4	1.04	24.6	0.97
-16 (1)	11	33.0	1.30	31.0	1.22
-20 (1 ¼)	11	41.9	1.65	39.6	1.56
-24 (1 ½)	11	47.8	1.88	45.5	1.79
-32 (2)	11	59.7	2.35	57.4	2.26

Seller Threads

Seller threads suit sealing pipe fittings well. These threads taper and fit tightly when tightened to the correct standard.

Seller threads are used in hydraulic and pneumatic applications to prevent leakage. Moreover, their form is helpful; to avoid loosening because of vibrations or pressure fluctuations.

Square Threads

Square Threads are flat and square-shaped threads with 90 degrees included angle. They provide excellent load-carrying capability and power transfer.

In addition, manufacturers use square threads in lead screws and mechanical drives. Because these threads reduce sliding and can endure high-pressure loads.

Square Thread Dimensions According to ISO Standards

Nominal Diameter (mm)	Pitch (mm)	Example Thread Type	Thread Configuration
22, 24, 26, 28	5	Sq 60×5	Single Start
30, 32, 36	6	Sq 60×6	Single Start
40, 44	7	Sq 60×7	Single Start
48, 50, 52	8	Sq 60×8	Single Start
55, 60	9	Sq 60×9	Single Start
65, 70, 75, 80	10	Sq 60×10	Single Start
85, 90, 95, 100	12	Sq 60×12	Single Start
Example with Lead		Sq 60×18(P9)LH	Two Start, Left Hand

ACME Threads

The ACME Threads contain a trapezoidal profile with an angle of 29 degrees. They offer a perfect proposition between power and performance. Engineers, ACME threads use in lead screws and linear actuators.

Since these threads have more space below and above the waves. Furthermore, they give more load-carrying capacity and minimize friction than square threads.

Acme Thread Designation and Dimensions

Designation	TPI	Tolerance Class	Major Dia. (in)	Pitch Dia. (in)	Minor Dia. (in)
1/4-16 Acme	16	2G	0.2500	0.2450	0.1775
1/4-16 Acme	16	3G	0.2500	0.2450	0.1775
5/16-14 Acme	14	2G	0.3125	0.3075	0.2311
5/16-14 Acme	14	3G	0.3125	0.3075	0.2311
3/8-12 Acme	12	2G	0.3750	0.3700	0.2817
3/8-12 Acme	12	3G	0.3750	0.3700	0.2817
1/2-10 Acme	10	2G	0.5000	0.4950	0.3800
1/2-10 Acme	10	3G	0.5000	0.4950	0.3800
5/8-8 Acme	8	2G	0.6250	0.6188	0.4800
5/8-8 Acme	8	3G	0.6250	0.6188	0.4800
3/4-6 Acme	6	2G	0.7500	0.7417	0.5633
3/4-6 Acme	6	3G	0.7500	0.7417	0.5633
1-5 Acme	5	2G	1.0000	0.9900	0.7800
1-5 Acme	5	3G	1.0000	0.9900	0.7800
1 1/4-5 Acme	5	2G	1.2500	1.2400	1.0300
1 1/4-5 Acme	5	3G	1.2500	1.2400	1.0300
2-4 Acme	4	2G	2.0000	1.9875	1.7300
2-4 Acme	4	3G	2.0000	1.9875	1.7300
3-2 Acme	2	2G	3.0000	2.9750	2.4800
3-2 Acme	2	3G	3.0000	2.9750	2.4800
4-2 Acme	2	2G	4.0000	3.9750	3.4800
4-2 Acme	2	3G	4.0000	3.9750	3.4800

Knuckle Threads

Knuckle Threads are convex form threads similar to the human knuckle. You can drill these threads for lids, caps, and hand tools. In addition, the rounded design of the threads works to reduce the possibility of cross-threading and guarantees a better fit.

Table: Knuckle TPI (Threads per Inch), pitch, and the various diameters (major, pitch, and minor) with their respective maximum and minimum values.

Thread Designation	TPI	Pitch (mm)	Major Diameter (mm)	Pitch Diameter (mm)	Minor Diameter (mm)	Max (mm)	Min (mm)	Max (mm)
Rd 8 x 1/10	10	2.540	8.000	7.665	6.730	6.530	5.460	5.210
Rd 9 x 1/10	10	2.540	9.000	8.665	7.730	7.530	6.460	6.210
Rd 10 x 1/10	10	2.540	10.000	9.665	8.730	8.530	7.460	7.210
Rd 11 x 1/10	10	2.540	11.000	10.665	9.730	9.530	8.460	8.210
Rd 12 x 1/10	10	2.540	12.000	11.665	10.730	10.530	9.460	9.210
Rd 14 x 1/8	8	3.175	14.000	13.625	12.730	12.494	10.825	10.525
Rd 16 x 1/8	8	3.175	16.000	15.625	14.412	14.176	12.825	12.525
Rd 18 x 1/8	8	3.175	18.000	17.625	16.412	16.176	14.825	14.525
Rd 20 x 1/8	8	3.175	20.000	19.625	18.412	18.176	16.825	16.525
Rd 22 x 1/8	8	3.175	22.000	21.625	20.412	20.176	18.825	18.525
Rd 24 x 1/8	8	3.175	24.000	23.625	22.412	22.176	20.825	20.525
Rd 26 x 1/8	8	3.175	26.000	25.625	24.412	24.176	22.825	22.525
Rd 28 x 1/8	8	3.175	28.000	27.625	26.412	26.176	25.825	25.525
Rd 30 x 1/8	8	3.175	30.000	29.625	28.412	28.176	26.825	26.525
Rd 32 x 1/8	8	3.175	32.000	31.625	30.412	30.176	28.825	28.525
Rd 34 x 1/8	8	3.175	34.000	33.625	32.412	32.176	30.825	30.525
Rd 36 x 1/8	8	3.175	36.000	35.625	34.412	34.176	32.825	32.525
Rd 38 x 1/8	8	3.175	38.000	37.625	36.412	36.176	34.825	34.525
Rd 40 x 1/6	6	4.233	40.000	39.525	37.883	37.583	35.767	35.392
Rd 42 x 1/6	6	4.233	42.000	41.525	39.883	39.583	37.767	37.392
Rd 44 x 1/6	6	4.233	44.000	43.525	41.883	41.583	39.767	39.392
Rd 46 x 1/6	6	4.233	46.000	45.525	43.883	43.583	41.767	41.392
Rd 48 x 1/6	6	4.233	48.000	47.525	45.883	45.583	43.767	43.392
Rd 50 x 1/6	6	4.233	50.000	49.525	47.883	47.583	45.767	45.392
Rd 52 x 1/6	6	4.233	52.000	51.525	49.883	49.583	47.767	47.392
Rd 55 x 1/6	6	4.233	55.000	54.525	52.883	52.583	50.767	50.392
Rd 58 x 1/6	6	4.233	58.000	57.525	55.883	55.583	53.767	53.392
Rd 60 x 1/6	6	4.233	60.000	59.525	57.883	57.583	55.767	55.392
Rd 62 x 1/6	6	4.233	62.000	61.525	59.883	59.583	57.767	57.392
Rd 65 x 1/6	6	4.233	65.000	64.525	62.883	62.583	60.767	60.392
Rd 68 x 1/6	6	4.233	68.000	67.525	65.883	65.583	63.767	63.392
Rd 70 x 1/6	6	4.233

Buttress Threads

Buttress Threads comprise an asymmetrical shape. These threads have a steep flank and a shallow flank. They intend to carry axial loads in one direction. Power transmission systems use buttress threads and place them in jacks and heavy equipment.

Butter Thread Standard Chart

Thread	Pitch diameter (mm)	Outer diameter – internal thread (mm)	Core diameter – External Thread (mm)	Core diameter – Internal Thread (mm)
S10x2	8.5	10	6.529	7
S12x2	10.5	12	8.529	9
S12x3	9.75	12	6.793	7.5
S14x2	12.5	14	10.529	11
S14x3	11.75	14	8.793	9.5
S16x2	14.5	16	12.529	13
S16x4	13	16	9.058	10
S18x2	16.5	18	14.529	15
S18x4	15	18	11.058	12
S20x2	18.5	20	16.529	17
S20x4	17	20	13.058	14
S22x3	19.75	22	16.793	17.5
S22x5	18.25	22	13.322	14.5
S22x8	16	22	8.116	10
S24x3	21.75	24	18.793	19.5
S24x5	20.25	24	15.322	16.5
S24x8	18	24	10.116	12
S26x3	23.75	26	20.793	21.5
S26x5	22.25	26	17.322	18.5
S26x8	20	26	12.116	14
S28x3	25.75	28	22.793	23.5
S28x5	24.25	28	19.322	20.5
S28x8	22	28	14.116	16
S30x3	27.75	30	24.793	25.5
S30x6	25.5	30	19.587	21
S30x10	22.5	30	12.645	15
S32x3	29.75	32	26.793	27.5
S32x6	27.5	32	21.587	23
S32x10	24.5	32	14.645	17
S34x3	31.75	34	28.793	29.5
S34x6	29.5	34	23.587	25
S34x10	26.5	34	16.645	19
S36x3	33.75	36	30.793	31.5
S36x6	31.5	36	25.587	27
S36x10	28.5	36	18.645	21
S38x3	35.75	38	32.793	33.5
S38x7	32.75	38	25.851	27.5
S38x10	30.5	38	20.645	23
S40x3	37.75	40	34.793	35.5
S40x7	34.75	40	27.851	29.5
S40x10	32.5	40	22.645	25
S42x3	39.75	42	36.793	37.5
S42x7	36.75	42	29.851	31.5
S42x10	34.5	42	24.645	27
S44x3	41.75	44	38.793	39.5
S44x7	38.75	44	31.851	33.5
S44x12	35	44	23.174	26
S46x3	43.75	46	40.793	41.5
S46x8	40	46	32.116	34
S46x12	37	46	25.174	28
S48x3	45.75	48	42.793	43.5
S48x8	42	48	34.116	36
S48x12	39	48	27.174	30
S50x3	47.75	50	44.793	45.5
S50x8	44	50	36.116	38
S50x12	41	50	29.174	32
S52x3	49.75	52	46.793	47.5
S52x8	46	52	38.116	40
S52x12	43	52	31.174	34
S55x3	52.75	55	49.793	50.5
S55x9	48.25	55	39.38	41.5
S55x14	44.5	55	30.702	34
S60x3	57.75	60	54.793	55.5
S60x9	53.25	60	44.38	46.5
S60x14	49.5	60	35.702	39
S65x4	62	65	58.058	59
S65x10	57.5	65	47.645	50
S65x16	53	65	37.231	41
S70x4	67	70	63.058	64
S70x10	62.5	70	52.645	55
S70x16	58	70	42.231	46
S75x4	72	75	68.058	69
S75x10	67.5	75	57.645	60
S75x16	63	75	47.231	51
S80x4	77	80	73.058	74
S80x10	72.5	80	62.645	65
S80x16	68	80	52.231	56
S85x4	82	85	78.058	79
S85x12	76	85	64.174	67
S85x18	71.5	85	53.76	58
S90x4	87	90	83.058	84
S90x12	81	90	69.174	72
S90x18	76.5	90	58.76	63
S95x4	92	95	88.058	89
S95x12	86	95	74.174	77
S95x18	81.5	95	63.76	68
S100x4	97	100	93.058	94
S100x12	91	100	79.174	82
S100x20	85	100	65.289	70
S105x4	102	105	98.058	99
S105x12	96	105	84.174	87
S105x20	90	105	70.289	75
S110x4	107	110	103.058	104
S110x12	101	110	89.174	92
S110x20	95	110	75.289	80
S115x6	110.5	115	104.587	106
S115x14	104.5	115	90.702	94
S115x22	98.5	115	76.818	82
S120x6	115.5	120	109.587	111
S120x14	109.5	120	95.702	99
S120x22	103.5	120	81.818	87
S125x6	120.5	125	114.587	116
S125x14	114.5	125	100.702	104
S125x22	108.5	125	86.818	92
S130x6	125.5	130	119.587	121
S130x14	119.5	130	105.702	109
S130x22	113.5	130	91.818	97

Worm Threads

Designers intend worm threads to be spiral in shape, similar to a screw. They frequently apply them in worm gears to reduce torque and increase mechanical advantage. Therefore, applications that need high reduction ratios and compact structures benefit most from these threads.

Worm Thread Profiles with Pitch Diameters, Diametral Pitch, and Other Specifications

Row	Typical Pitch Diameter (inches)	Diametral Pitch (DP)	Pitch (n/DP)	Addendum (1/DP)	Whole Depth (Pitch x 0.686)	Worm Thread Profile
1	3.000	4	0.7854	0.2500	0.5388	Worm Thread Profile – 3.000
2	2.500	5	0.6283	0.2000	0.4310	Worm Thread Profile – 2.500
3	2.000	6	0.5236	0.1667	0.3592	Worm Thread Profile – 2.000
4	1.750	7	0.4488	0.1429	0.3079	Worm Thread Profile – 1.750
5	1.500	8	0.3927	0.1250	0.2694	Worm Thread Profile – 1.500
6	1.375	9	0.3491	0.1111	0.2395	Worm Thread Profile – 1.375
7	1.250	10	0.3142	0.1000	0.2155	Worm Thread Profile – 1.250
8	1.125	11	0.2856	0.0909	0.1959	Worm Thread Profile – 1.125
9	1.000	12	0.2618	0.0833	0.1796	Worm Thread Profile – 1.000
10	0.813	14	0.2244	0.0714	0.1539	Worm Thread Profile – 0.813
11	0.625	16	0.1963	0.0625	0.1347	Worm Thread Profile – 0.625
12	0.583	18	0.1745	0.0556	0.1197	Worm Thread Profile – 0.583
13	0.542	20	0.1571	0.0500	0.1078	Worm Thread Profile – 0.542
14	0.500	24	0.1309	0.0417	0.0898	Worm Thread Profile – 0.500
15	0.469	28	0.1122	0.0357	0.0700	Worm Thread Profile – 0.469
16	0.438	32	0.0982	0.0313	0.0673	Worm Thread Profile – 0.438
17	0.407	40	0.0785	0.0250	0.0539	Worm Thread Profile – 0.407
18	0.375	48	0.0654	0.0208	0.0449	Worm Thread Profile – 0.375

Single & Multi Threads

Single Threads have only one line of thread along the entire fastener length.

Engineers mainly apply them to normal bolts, screws, and other fasteners used in the construction industry.

Multiple Threads, on the other hand, multiple threads include several threads along the same length. They expand the engagement area and enable faster threading. You can use multi-threads in high-speed or high-load applications where assembly time is a major concern.

Standard Design Table for Single & Multi Threads

Thread Type	Nominal Diameter (mm)	Pitch (mm)	Threads per Inch (TPI)	Core Diameter (External Thread)	Core Diameter (Internal Thread)	Major Diameter (External Thread)	Pitch Diameter (Internal Thread)	Thread Depth (mm)	Thread Profile
Single Thread	5.0	0.8	32	4.2	4.8	5.0	4.6	0.4	ISO 68°
Single Thread	8.0	1.0	25	6.9	7.1	8.0	7.6	0.5	ISO 60°
Single Thread	10.0	1.5	20	8.5	9.0	10.0	9.7	0.6	ISO 60°
Single Thread	12.0	1.75	18	10.1	10.6	12.0	11.5	0.7	ISO 60°
Multi Thread	8.0	1.25	24	6.5	6.9	8.0	7.8	0.45	ISO 60°
Multi Thread	12.0	2.0	15	10.8	11.3	12.0	11.9	0.8	ISO 60°
Multi Thread	15.0	2.5	12	13.5	14.0	15.0	14.8	1.0	ISO 60°
Multi Thread	20.0	3.0	10	18.0	18.6	20.0	19.8	1.2	ISO 60°
Multi Thread	25.0	3.5	8	22.3	22.9	25.0	24.8	1.5	ISO 60°
Multi Thread	30.0	4.0	6	27.4	28.1	30.0	29.8	1.8	ISO 60°

Material Strength and Hardness Properties for Threading and Drilling

Material	Specification	Tensile Strength (psi)	Yield Strength (psi)	Shear Strength (psi)	Elongation	Brinell Hardness (BHN)	Rockwell Hardness
Aluminum 6061-T6	ASTM B211	45,000	40,000	22,500	17%	BHN 95	B56
Brass 360	ASTM B16	58,000	45,000	29,000	25%	BHN 143	B78
Nickel Alloy 405 (Monel)	ASTM B164	85,000	60,000	42,500	24%	BHN 163	B85
Stainless Steel 18-8 (303)	ASTM A582	90,000	35,000	45,000	50%	BHN 160	B83
Stainless Steel 316	ASTM A276	75,000	30,000	37,500	45%	BHN 160	B83
Steel 12L14	ASTM A108	78,000	60,000	39,000	15%	BHN 160	B84
Steel Alloy C4140/41L40	ASTM A108 Cold	105,000	85,000	52,500	15%	BHN 187	B91
Steel Alloy C4140/41L40	ASTM A108 Thru Hard	140,000	105,000	70,000	n/a	BHN 300	B91

Considerations For Selecting The Right Type of Thread

For choosing the right type, consider the following factors to make the choice easier;

• Application Requirements: Choose the thread type by considering the load, torque, and environmental conditions of the application. For instance, manufacturers utilize to accomplish leak-proof joints, and V-threads provide mechanical fastening joints.
• Material Compatibility: Soft materials may need thinner threads than hard materials which need thick threads.
• Thread Strength: You can consider the actual load as desired. Generally, coarse threads bear higher resistance levels to stripping and fine threads which are optimal for confined areas.
• Assembly Speed: Use multi-threaded fasteners, if you need quick assembling. Because they are relatively faster to engage than single-threaded.
• Durability and Wear Resistance: In cases of frequent usage, apply thread types like the ‘Acme the Buttress threads’ because these types of threads can easily withstand higher loads and resist wearing effectively.

Summary

To sum up, the ultimate selection of thread depends on requirements for mechanical connections and structural aspects. Other factors to bear in micro thread design include the specific application requirements, material compatibility with interference thread, and the strength and rigor required of the threads. Taper, V-shaped, and ACME standard threads feature different benefits according to the load-carrying capability, sealing adequacy, and accuracy degree.

Moreover, the decision of whether to employ a single-threaded or multi-threaded design can make a difference of tens of seconds in the time needed to assemble. Therefore, it’s possible to select threads according to functional and operational requirements, which will guarantee their further stability and effectiveness in the long run.

Choosing right tap drill size is critical to ensure parts to be threaded, and guarantee their function. And it is same important for CNC machining.

FAQ’s

Q1. What is the difference between coarse and fine threads?

Coarse threads are wider and deeper compared to fine threads. Therefore these threads are less likely to strip. In contrast, thin pitches also mean smaller diameter threads, with more threads to the inch, which makes for a closer fit.

Q2. How do I choose the correct tap drill size?

You can obtain the correct tap drill size by subtracting the thread pitch from the major diameter of the fastener. For instance, for an M10 x 1.5 thread, the tap drill size would be equal to M10 – 1.5 mm = 8.5 mm. Though recommended tap drill sizes vary from table to table.

Q3. What are the benefits of using taper threads?

Taper threads produce pressure-tight joints through thread wedging. Moreover, they provide leak-proof features and are notable in systems where high pressure or vibration is usual.

Q4. Why do engineers prefer ACME threads in lead screws?

ACME threads are of trapezoidal cross-sections. These threads hold fair strength, load-carrying capacity, and minimum friction. They commonly use lead screws in linear motion applications. Lead screws can sustain high axial loads. They also provide a smooth operational profile over time.