Screws have a gauge based on their diameter, just like wires and shotguns. A screw is named according to its diameter followed by the number of threads per inch. The ubiquitous 1/4-20 machine screw, for example, has 20 threads per inch and a 1/4 inch diameter. The 1/4-20, however, does not use the screw gauge scale. Screws that do include the 10-32, 8-32, etc.

Unlike wire, shotgun, and drill gauges, screw gauges go up with larger diameter, and it does not seem to be exactly standardized. The following are some screw gauge sizes, in inches:

2       .0875-.084
3       .101-.097
4       .1145-.110
5       .1275-.123
6       .141-.135
8       .167-.162
10       .194-.189
12       .220-.215

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