SAE Tap & Drill Chart

The twist drill bit was invented by Steven A. Morse of East Bridgewater, MA, in 1861. He received U.S. Patent 38,119 for his invention on April 7, 1863. The original method of manufacture was to cut two grooves in opposite sides of a round bar, then to twist the bar to produce the helical flutes. This gave the tool its name.

Nowadays, the drill bit is usually made by rotating the bar while moving it past a grinding wheel to cut the flutes in the same manner as cutting helical gears. Tools recognizable as twist drill bits are currently produced in diameters covering a range from 0.05 mm (0.002") to 100 mm (4"). Lengths up to about 1000 mm (39") are available for use in powered hand tools.

The geometry and sharpening of the cutting edges is crucial to the performance of the bit. Users often throw away small bits that become blunt, and replace them with new bits, because they are inexpensive and sharpening them well is difficult. For larger bits, special grinding jigs are available. A special tool grinder is available for sharpening or reshaping cutting surfaces on twist drills to optimize the drill for a particular material. -Wikipedia

Standard SAE (Society of Automotive Engineers) tap & drill size chart.

Thread Size	Drill Diameter (in)	Tap Drill Size	Thread Size	Drill Diameter (in)	Tap Drill Size
Coarse Thread			Fine Thread
1-64	.0595	No. 53	0-80	.0469	3/64
2-56	.0700	No. 50	1-72	.0595	No. 53
3-48	.0785	No. 47	2-64	.0700	No. 50
4-40	.0890	No. 43	3-56	.0820	No. 45
5-40	.1015	No. 38	4-48	.0935	No. 42
6-32	.1065	No. 36	5-44	.1040	No. 37
8-32	.1360	No. 29	6-40	.1130	No. 33
10-24	.1495	No. 25	8-36	.1360	No. 29
12-24	.1770	No. 16	10-32	.1590	No. 21
1/4-20	.2010	No. 7	12-28	.1820	No. 14
5/16-18	.2570	'F'	1/4-28	.2130	No. 3
3/8-16	.3125	5/16	5/16-24	.2720	'I'
7/16-14	.3680	'U'	3/8-24	.3320	'Q'
1/2-13	.4219	27/64	7/16-20	.3906	25/64
9/16-12	.4844	31/64	1/2-20	.4531	29/64
5/8-11	.5312	17/32	9/16-18	.5156	33/64
3/4-10	.6562	21/32	5/8-18	.5781	37/64
7/8-9	.7656	49/64	3/4-16	.6875	11/16
1"-8	.8750	7/8	7/8-14	.8125	13/16
			1"-14	.9375	59/64

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