Determining screw/thread size

[DonRotolo]

Screws come even smaller, #0000 - 160 at Small Parts.They're about $4 each, and made by elves.

So, to elaborate on Tristan's explanation: First measure the bolt's outside diameter, then measure the distance between thread ridges (I usually measure 10 and divide, better accuracy), then measure the length from the bottom of the head to the end.

The diameter won't be exact, but pretty close to the bolt "dimension" - for example a 1/2" bolt might measure just a bit under 0.500. Then threads per inch, then length. Specify the head style and material, and there's little else to describe it by. (Actually, you can classify it further by strength and thread finish. But that's all there is, I think)

After a while, you can tell by looking at it. If you have an extra $10, go to the hardware store and ask to buy one of each size bolt (pick a common length, like 1 inch), as you keep them around you'll get used to the sizes. Then you can sort all those bolts in that old coffee can....

Don