Screw Thread Chart

Metric (ISO)

Size	Coarse pitch (mm)	Tap drill (mm)	Fine pitch (mm)	Tap drill (mm)
M1.6	0.35	1.25	-	-
M2	0.4	1.6	-	-
M2.5	0.45	2.05	-	-
M3	0.5	2.5	-	-
M4	0.7	3.3	-	-
M5	0.8	4.2	-	-
M6	1	5	-	-
M8	1.25	6.75	1	7
M10	1.5	8.5	1.25	8.75
M12	1.75	10.25	1.25	10.75
M14	2	12	1.5	12.5
M16	2	14	1.5	14.5
M18	2.5	15.5	1.5	16.5
M20	2.5	17.5	1.5	18.5
M22	2.5	19.5	1.5	20.5
M24	3	21	2	22

Unified (UNC / UNF)

Size	Diameter (in)	UNC (TPI)	Tap drill (in)	UNF (TPI)	Tap drill (in)
#0	0.0600	-	-	80	0.0475
#1	0.0730	64	0.0574	72	0.0591
#2	0.0860	56	0.0681	64	0.0704
#3	0.0990	48	0.0782	56	0.0811
#4	0.1120	40	0.0870	48	0.0912
#5	0.1250	40	0.1000	44	0.1023
#6	0.1380	32	0.1068	40	0.1130
#8	0.1640	32	0.1328	36	0.1362
#10	0.1900	24	0.1483	32	0.1588
#12	0.2160	24	0.1743	28	0.1803
1/4	0.2500	20	0.2000	28	0.2143
5/16	0.3125	18	0.2569	24	0.2708
3/8	0.3750	16	0.3125	24	0.3333
7/16	0.4375	14	0.3661	20	0.3875
1/2	0.5000	13	0.4231	20	0.4500
9/16	0.5625	12	0.4792	18	0.5069
5/8	0.6250	11	0.5341	18	0.5694
3/4	0.7500	10	0.6500	16	0.6875
7/8	0.8750	9	0.7639	14	0.8036
1	1.0000	8	0.8750	12	0.9167

How to use Screw Thread Chart

Find the metric or unified size.
Read the pitch or threads per inch, and the tap drill.

Frequently asked questions

How is the tap drill size worked out?

As the major diameter minus the pitch (metric) or minus 1 / TPI (unified), which gives about 75% thread. Round to the nearest drill you have.

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