Tap Drill Sizes

Some explanation:

What kind of tap do I need? As explained in the screw guide, coarse threads are much more common, stronger, less likely to jam during installation (cross thread), and faster to install. So, if you're deciding between coarse and fine threads for a custom hole, use a coarse thread unless you're going into sheet metal. If you're trying to make a hole for an unidentified screw, chances are it's a coarse thread. Metric coarse threads are in between English coarse and fine threads. Metric fine threads are finer than English fine threads and are rarely used.

50% vs 75% tap drill sizes: 100% engagement of a male and female thread means that both threads are fully formed and fully engaged. 50% means that only half of the thread height is engaged, and is what you'd have if you ground off the top half of a fully formed thread. According to the machinery's handbook, tests have shown that more than 60% thread engagement provides no significant increase in strength. For thread engagements more than 1.5 diameters deep, 50% is usually sufficient. Most taps drill are sized to drill a slightly larger hole than what a 100% thread could be cut into, typically 75% or 50%. More commonly, holes that will create a 75% thread when tapped are used as a margin of safety, and this is what we sell. The downside with drilling a hole that a 100% thread could be tapped into is that it is much more difficult to tap (deeper cuts into the metal), and therefore much more likely to break a tap. We recommend 75% tapping drills unless deep holes in steel are being made.

Clearance holes: A clearance hole is large enough for the screw to slide through without being turned. Many tapping charts will have two types of clearance drills: tight and loose. We list the tight clearance drills and recommend choosing whatever bit is handy and larger than the major diameter for larger clearances--just make sure the screw head or washer is larger. Note that if several holes are being made, the tight clearances don't leave much room for misaligned holes.

Coarse Threads - English

tap size  (major dia. - threads / inch)	screw  major dia.	tap drill size  for 75% .dia	tap drill size for 50% .dia	clearance drill
#0-80	0.060	3/64 (.0469)	55 (.0520)	50 (.0700)
#1-64	0.073	53 (.0595)	1/16 (.0625)	46 (.0810)
#2-56	0.086	50 (.0700)	49 (.0730)	41 (.0960)
#3-48	0.099	47 (.0785)	44 (.0860)	35 (.1100)
#4-40	0.112	43 (.0890)	41 (.0960)	30 (.1285)
#5-40	0.125	38 (.1015)	7/64 (.1094)	29 (.1360)
#6-32	0.138	36 (.1065)	32 (.1160)	25 (.1495)
#8-32	0.164	29 (.1360)	27 (.1440)	16 (.1770)
#10-24	0.190	25 (.1495)	20 (.1610)	7 (.2010)
#12-24	0.216	16 (.1770)	12 (.1890)	1 (.2280)
1/4-20	.2500	7 (.2010)	7/32 (.2188)	H (.2660)
5/16-18	.3125	F (.2570)	J (.2770)	Q (.3320)
3/8-16	.3750	5/16 (.3125)	Q (.3320)	X (.3970)
7/16-14	.4375	U (.3680)	25/64 (.3906)	15/32 (.4687)
1/2-13	.5000	27/64 (.4219)	29/64 (.4531)	17/32 (.5312)
9/16-12	.5625	31/64 (.4844)	33/64 (.5156)	19/32 (.5938)
5/8-11	.6250	17/32 (.5312)	9/16 (.5625)	21/32 (.6562)
3/4-10	.7500	21/32 (.6562)	11/16 (.6875)	25/32 (.7812)
7/8-9	.8750	49/64 (.7656)	51/64 (.7969)	29/32 (.9062)
1"-8	1.000	7/8 (.8750)	59/64 (.9219)	1-1/32 (1.0313)
1 1/8-7	1.1250	63/64 (.9844)	1-1/32 (1.0313)	1-5/32 (1.1562)

Coarse Threads - Metric

tap size	major dia.  mm (inch)	tap drill (mm)	tap drill  (inch)	clearance (mm)	clearance inch (dec.)
M1.6x0.35	1.6 (.0630)	1.25	#55	1.8	#49
M2x0.4	2.0 (.0787)	1.60	#52	2.4	#41
M2.5x0.45	2.5 (.0984)	2.05	#46	2.9	#32
M3x.05	3.0 (.1181)	2.50	#39	3.4	#29
M3.5x0.6	3.5 (.1378)	2.90	#32	3.9	#23
M4x0.7	4.0 (.1575)	3.30	#30	4.5	#16
M5x0.8	5.0 (.1969)	4.20	#19	5.5	7/32
M6x1	6.0 (.2362)	5.0	#8	6.6	G
M8x1	8.0 (.3150)	7.0	J	9.0	T
M10x1.25	10.0 (.3937)	8.8	11/32	12.0	31/64
M12x1.25	12.0 (.4724)	10.8	27/64	14.0	35/64
M14x1.5	14.0 (.5512)	12.5	1/2	16.0	5/8
M16x1.5	16.0 (.6299)	14.5	37/64	18.0	45/64
M18x1.5	18.0 (.7087)	16.5	21/32	20.0	51/64
M20x1.5	20.0 (.7874)	18.5	47/64	22.0	7/8
M22x1.5	22.0 (.8661)	20.5	13/16	25.0	1
M24x2	24.0 (.9449)	22.0	7/8	27.0	1-5/64
M27x2	27.0 (1.0630)	25.0	1	30.0	1-3/16

Fine Threads - English

tap size  (major dia. - threads / inch)	screw  major dia.	tap drill size  for 75% .dia	tap drill size for 50% .dia	clearance drill
#1-72	0.073	53 (.0595)	52 (.0635)	46 (.0810)
#2-64	0.086	50 (.0700)	48 (.0760)	41 (.0960)
#3-56	0.099	45 (.0820)	43 (.0890)	35 (.1100)
#4-48	0.112	42 (.0935)	40 (.0980)	30 (.1285)
#5-44	0.125	37 (.1040)	35 (.1100)	29 (.1360)
#6-40	0.138	33 (.1130)	31 (.1200)	25 (.1495)
#8-36	0.164	29 (.1360)	26 (.1470)	16 (.1770)
#10-32	0.190	21 (.1590)	18 (.1695)	7 (.2010)
#12-28	0.216	14 (.1820)	10 (.1935)	1 (.2280)
1/4-28	.2500	3 (.2130)	1 (.2280)	H (.2660)
5/16-24	.3125	I (.2720)	9/32 (.2812)	Q (.3320)
3/8-24	.3750	Q (.3320)	S (.3480)	X (.3970)
7/16-20	.4375	25/64 (.3906)	13/32 (.4062)	15/32 (.4687)
1/2-20	.5000	29/64 (.4531)	15/32 (.4688)	17/32 (.5312)
9/16-18	.5625	33/64 (.5156)	17/32 (.5312)	19/32 (.5938)
5/8-18	.6250	37/64 (.5781)	19/32 (.5938)	21/32 (.6562)
3/4-16	.7500	11/16 (.6875)	45/64 (.7031)	25/32 (.7812)
7/8-14	.8750	13/16 (.8125)	53/64 (.8281)	29/32 (.9062)
1"-12	1.000	15/16 (.9375)	61/64 (.9531)	1-1/32 (1.0313)
1 1/8-12	1.1250	1-3/64 (1.0469)	1-5/64 (1.0781)	1-5/32 (1.1562)

Fine Threads - Metric

tap size	major dia.  mm (inch)	tap drill (mm)	tap drill  (inch)	clearance (mm)	clearance inch (dec.)
M8x1.25	8.0 (.3150)	6.8	H	9.0	T
M10x1.5	10.0 (.3937)	8.5	R	12.0	31/64
M12x1.75	12.0 (.4724)	10.2	13/32	14.0	35/64
M14x2	14.0 (.5512)	12.0	15/32	16.0	5/8
M16x2	16.0 (.6299)	14.0	35/64	18.0	45/64
M18x2.5	18.0 (.7087)	15.5	39/64	20.0	51/64
M20x2.5	20.0 (.7874)	17.5	11/16	22.0	7/8
M22x2.5	22.0 (.8661)	19.5	49/64	25.0	1
M24x3	24.0 (.9449)	21.0	53/64	27.0	1-5/64
M27x3	27.0 (1.0630)	24.0	1	15/16	1-3/16

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