Tap Drills for Number Machine Screws -- Technical Notes

Fabrication

Number	Threads /Inch	Series	Nom. Dia. (in)	Drill Size (65-75% thread)	Equivalents		Close Fit		Free Fit
Screw Size				Tapping Drills			Clearance Drills
Number	Threads /Inch	Series	Nom. Dia. (in)	Drill Size (65-75% thread)	(decimal)	(mm)	Drill Size	Dec. Equiv.	Drill Size	Dec. Equiv.

000	120		0.0340	71	0.0260	0.6604	65	0.0350	62	0.0380
00	90		0.0470	65	0.0350	0.8890	3/64"	0.0469	55	0.0520
0	80	NF	0.0600	3/64"	0.0469	1.1913	52	0.0635	50	0.0700
1	56	NS	0.0730	54	0.0550	1.3970	48	0.0760	46	0.0810
	64	NC		53	0.0595	1.5113
	72	NF		53	0.0595	1.5113
2	56	NC	0.0860	50	0.0700	1.7780	43	0.0890	41	0.0960
2	64	NF	0.0860	50	0.0700	1.7780	43	0.0890	41	0.0960
3	48	NC	0.0990	47	0.0785	1.9939	37	0.1040	35	0.1100
3	56	NF	0.0990	45	0.0820	2.0828	37	0.1040	35	0.1100
4	36	NS	0.1120	44	0.0860	2.1844	32	0.1160	30	0.1285
	40	NC		43	0.0890	2.2606
	48	NF		42	0.0935	2.3749
5	40	NC	0.1250	38	0.1015	2.5781	30	0.1285	29	0.1360
5	44	NF	0.1250	37	0.1040	2.6416	30	0.1285	29	0.1360
6	32	NC	0.1380	36	0.1065	2.7051	27	0.1440	25	0.1495
	36	NS		34	0.1110	2.8194
	40	NF		33	0.1130	2.8702
8	32	NC	0.1640	29	0.1360	3.4544	18	0.1695	16	0.1770
	36	NF		29	0.1360	3.4544
	40	NS		28	0.1405	3.5687
10	24	NC	0.1900	25	0.1495	3.7973	9	0.1960	7	0.2010
	30	NS		22	0.1570	3.9878
	32	NF		21	0.1590	4.0386
12	24	NC	0.2160	16	0.1770	4.4958	2	0.2210	1	0.2280
	28	NF		14	0.1820	4.6228
	32	NEF		13	0.1850	4.6990
14	20	NS	0.2420	10	0.1935	4.9149	D	0.2460	F	0.2570
14	24	NS	0.2420	7	0.2010	5.1054	D	0.2460	F	0.2570

Number	Threads /Inch	Series	Nom. Dia. (in)	Drill Size (65-75% thread)	(decimal)	(mm)	Drill Size	Dec. Equiv.	Drill Size	Dec. Equiv.
Number	Threads /Inch	Series	Nom. Dia. (in)	Drill Size (65-75% thread)	Equivalents		Close Fit		Free Fit
Screw Size				Tapping Drills			Clearance Drills

Thread Series: National Coarse (NC); National Fine (NF); National Extra Fine (NEF); National Special (NS)

1 inch = 25.4 millimeters

Tap Drill Size (65-75% thread) = Nominal Diameter - One Pitch Length: example: Tap Drill for #6-32 NC screw is #36, closest drill to 0.1067 inches (0.1067 = 0.1380 - 0.0313)

Nominal Diameter of Number Screw (in.) = (Screw Number x 0.0130) + 0.0600: example: Nominal Diameter of #6 screw is 0.1380 inches [0.1380 = (6 x 0.0130) + 0.0600]

Pitch (in.) = 1 / (Threads per Inch): example: Pitch of 32 threads per inch is 0.0313 inches (0.0313 = 1/32)

JavaScript Calculators
- Inch/Millimeter
- Tapping Drill Size
- Nominal Diameter of Number Screw
- Pitch
Tapping and Clearance Drills
- Fractional Machine Screws
- Metric Machine Screws
Drill Size Conversions
Starrett Reference Tables
Download the table as:
- An Abode PDF file
- A zipped Microsoft Excel spreadsheet

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Page author: Dawn Rorvik (rorvikd@evergreen.edu)
Last modified: 05/20/2003