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By thisisjaye
when you get into sizing of bolts, anything under 1/4 of an in is given a number. a number "6" bolt/screw is closest to 1/8th in. and the most common size thread for a 6 is "32" which means 32 threads per inch. It will be written out like this "6-32". The length will be noted on the package and there are many head styles to choose from. If you would like to browse through all your options go here - this will walk you through all the sizing options and has a very easy layout to fallow. to figure it out the less technically way, you could always bring what your trying to figure out to Lowes or home depot and use trial and error.

best of luck,
By Chagrin
The screws that hold the faceplates onto switches/outlets are 6-32 (at least in the US). If the screw matches, well you're done. If the screws in your claw are slightly thicker in diameter but the threads match, then look for 8-32 or, larger yet, 10-32.

At a hardware store these will be referred to as "machine screws".