Drills and Taps

What are Drills and Taps?

Think of it like this:

1. Drill: You use a drill to make a hole

   

2. Tap: You use a tap to cut threads on the inside of that hole, so you can screw a bolt into it.

   

So, you drill the hole first, then tap it to add the threads.

Key Terms

• O.D. (Outer Diameter): The width across the outside of an object. For a drill bit, it's the width of the cutting part.
• Tap (Tap Drill Size): The specific drill bit size used before threading a hole. Drill this hole first, then use a tap tool to cut threads.
• Close Fit: A hole drilled just slightly larger than the bolt, so the bolt fits snugly.
• Free Fit: A hole drilled larger than the bolt, allowing the bolt to pass through easily.

Drill and tap chart

Screw Size Thread	O.D. Decimal	Tap Size	Decimal	Close Fit Size	Decimal	Free Fit Size	Decimal
000-120	0.0340	71	0.0260	65	0.0350	62	0.0380
00-90	0.0410	65	0.0350	3/64"	0.0469	55	0.0520
0-80	0.0600	3/64" (56)	0.0469	52	0.0635	50	0.0700
1-72	0.0730	53	0.0595	48	0.0760	46	0.0810
2-56	0.0860	50	0.0700	43	0.0890	41	0.0960
3-48	0.099	47	0.0790	37	0.1040	36	0.1065
4-40	0.1120	43	0.0890	32	0.1160	30	0.1285
5-40	0.125	38	0.102	29	0.1360	28 (9/64)	0.1405
6-32	0.1380	36	0.1065	27	0.1440	25	0.1495
8-32	0.1640	29	0.1360	18 (11/64)	0.1695	16	0.1770
10-24	0.190	25	0.150	9	0.196	7 (13/64)	0.2010
10-32	0.1900	21	0.1590	9	0.1960	7 (13/64)	0.2010
1/4-20	0.2500	7	0.2010	F	0.2570	H (17/64)	0.2660
1/4-28	0.2500	3	0.2130	F	0.2570	H (17/64)	0.2660
5/16-18	0.3125	F	0.2570	P	0.3230	Q	0.3320
3/8-16	0.3750	5/16"	0.3125	W	0.3860	X	0.3970
1/2-13	0.5000	27/64"	0.4219	33/64"	0.5156	17/32"	0.5312

*For copper, aluminum, cast iron, bakelite, or very thin materials, use one drill size larger (i.e. a slightly smaller diameter).

Argos Color code