Tap & Clearance Drill Sizes — Imperial

Inch / UNC / UNF tap and clearance drill sizes. Shows 75% thread (aluminum, brass, plastics) and 50% thread (steel, stainless, iron) tap drills plus Close Fit and Free Fit clearance drills for every screw size from #0 to 1 inch.

Reference Reference Updated Apr 24, 2026

Tap and clearance drill sizes for inch threads (UNC / UNF). 75% thread drills are used for soft materials — aluminum, brass, plastics — where cleaner chip flow matters more than holding strength. 50% thread drills are preferred for steels and stainless where torque on the tap must stay low. Close Fit clearance holes are for precision assemblies; Free Fit allows some misalignment.

Screw Size	Major Diameter	Threads Per Inch	Minor Diameter	Tap Drill				Clearance Drill
				75% Thread Aluminum · Brass · Plastics		50% Thread Steel · Stainless · Iron		Close Fit		Free Fit
				Drill Size	Decimal Equiv.	Drill Size	Decimal Equiv.	Drill Size	Decimal Equiv.	Drill Size	Decimal Equiv.
0	.0600	80	.0447	3/64	.0469	55	.0520	52	.0635	50	.0700
1	.0730	64	.0538	53	.0595	1/16	.0625	48	.0760	46	.0810
1	.0730	72	.0560	53	.0595	52	.0635	48	.0760	46	.0810
2	.0860	56	.0641	50	.0700	49	.0730	43	.0890	41	.0960
2	.0860	64	.0668	50	.0700	48	.0760	43	.0890	41	.0960
3	.0990	48	.0734	47	.0785	44	.0860	37	.1040	35	.1100
3	.0990	56	.0771	45	.0820	43	.0890	37	.1040	35	.1100
4	.1120	40	.0813	43	.0890	41	.0960	32	.1160	30	.1285
4	.1120	48	.0864	42	.0935	40	.0980	32	.1160	30	.1285
5	.1250	40	.0943	38	.1015	7/64	.1094	30	.1285	29	.1360
5	.1250	44	.0971	37	.1040	35	.1100	30	.1285	29	.1360
6	.1380	32	.0997	36	.1065	32	.1160	27	.1440	25	.1495
6	.1380	40	.1073	33	.1130	31	.1200	27	.1440	25	.1495
8	.1640	32	.1257	29	.1360	27	.1440	18	.1695	16	.1770
8	.1640	36	.1299	29	.1360	26	.1470	18	.1695	16	.1770
10	.1900	24	.1389	25	.1495	20	.1610	9	.1960	7	.2010
10	.1900	32	.1517	21	.1590	18	.1695	9	.1960	7	.2010
12	.2160	24	.1649	16	.1770	12	.1890	2	.2210	1	.2280
		28	.1722	14	.1820	10	.1935
		32	.1777	13	.1850	9	.1960
1/4	.2500	20	.1887	7	.2010	7/32	.2188	F	.2570	H	.2660
		28	.2062	3	.2130	1	.2280
		32	.2117	7/32	.2188	1	.2280
5/16	.3125	18	.2443	F	.2570	J	.2770	P	.3230	Q	.3320
		24	.2614	I	.2720	9/32	.2812
		32	.2742	9/32	.2812	L	.2900
3/8	.3750	16	.2983	5/16	.3125	Q	.3320	W	.3860	X	.3970
		24	.3239	Q	.3320	S	.3480
		32	.3367	11/32	.3438	T	.3580
7/16	.4375	14	.3499	U	.3680	25/64	.3906	29/64	.4531	15/32	.4687
		20	.3762	25/64	.3906	13/32	.4062
		28	.3937	Y	.4040	Z	.4130
1/2	.5000	13	.4056	27/64	.4219	29/64	.4531	33/64	.5156	17/32	.5312
		20	.4387	29/64	.4531	15/32	.4688
		28	.4562	15/32	.4688	15/32	.4688
9/16	.5625	12	.4603	31/64	.4844	33/64	.5156	37/64	.5781	19/32	.5938
		18	.4943	33/64	.5156	17/32	.5312
		24	.5114	33/64	.5156	17/32	.5312
5/8	.6250	11	.5135	17/32	.5312	9/16	.5625	41/64	.6406	21/32	.6562
		18	.5568	37/64	.5781	19/32	.5938
		24	.5739	37/64	.5781	19/32	.5938
11/16	.6875	24	.6364	41/64	.6406	21/32	.6562	45/64	.7031	23/32	.7188
3/4	.7500	10	.6273	21/32	.6562	11/16	.6875	49/64	.7656	25/32	.7812
		16	.6733	11/16	.6875	45/64	.7031
		20	.6887	45/64	.7031	23/32	.7188
13/16	.8125	20	.7512	49/64	.7656	25/32	.7812	53/64	.8281	27/32	.8438
7/8	.8750	9	.7387	49/64	.7656	51/64	.7969	57/64	.8906	29/32	.9062
		14	.7874	13/16	.8125	53/64	.8281
		20	.8137	53/64	.8281	27/32	.8438
15/16	.9375	20	.8762	57/64	.8906	29/32	.9062	61/64	.9531	31/32	.9688
1	1.000	8	.8466	7/8	.8750	59/64	.9219	1-1/64	1.0156	1-1/32	1.0313
		12	.8978	15/16	.9375	61/64	.9531
		20	.9387	61/64	.9531	31/32	.9688

How to read this chart

Pick your screw size (e.g. 1/4) and thread pitch (e.g. 20 TPI → 1/4-20 UNC).
Choose between the 75% thread and 50% thread columns based on material. 75% gives full strength but high tap torque; 50% reduces tap breakage risk and is standard in production.
Use a letter- or number-drill gauge to identify sizes like "F" (0.257") or "#7" (0.201").
Always deburr and chamfer holes before tapping. A taper tap is most forgiving for hand-tapping; plug or bottoming taps are for blind holes.
For through-hole assembly, pick the Close or Free Fit column to drill the other piece.

Tap drill rules of thumb

75% thread: Tap Dia = Major − (1 / TPI). Full-strength standard; use for threads that must hold load.
50% thread: Tap Dia = Major − (1.3 / TPI). Halves tap torque; use for hard or gummy materials.
Formulaic swap: Shifting from 75% → 50% costs ~10% thread strength but can cut tap breakage by 60-70%.
Lubrication: Cutting oil on steel / stainless. Neat kerosene on aluminum. Dry on cast iron (chips clear themselves).

Notes

Data consolidated from machinist reference tables (LittleMachineShop reference, Machinery's Handbook). For a metric version see the companion Metric Tap & Clearance Drill Sizes tool.

Last updated: April 24, 2026