Screw Hole Sizes

This comes from this document, saved here for posterity. Originally comes from ASME, and The Machinist’s Handbook has more data.

screw diameter = (size number * 0.013”) + 0.060”

e.g. a #4-40 screw has a diameter of (4 * 0.013”) + 0.060” or 0.112”, and a #10 screw has a diameter of 0.190” (i.e. (10 * 0.013”) + 0.060”)

To find an appropriate hole clearance, add three times the the screw size number (in thou). That #4 screw would have a hole of 0.125” (0.112” + 3 * 0.004”).

Screw Size Major Dia. Hole Size Nearest Drill
2 0.086 0.092 3/32
4 0.112 0.125 1/8
6 0.138 0.156 5/32
8 0.164 0.188 3/16
10 0.190 0.210 13/64 or 7/32
12 0.216 0.246 1/4
For fractional screws:
Screw Size Major Dia. Hole Size Nearest Drill
1/4 0.250 0.281 9/32
5/16 0.312 0.328 21/64
3/8 0.375 0.390 25/64 or 13/32

The second page of the attached pdf goes into some of the theory behind holes in manufacturing which I think is actually quite interesting. Lots of things that nobody doing one-offs ever thinks about but which become pretty important when you want to make thousands or millions of the same thing and be able to maintain it out in the field.

Hole_sizes_for_screws.pdf (18 KB) Andrew Kohlsmith, 04/17/2013 04:25 PM

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