If you can't find the guage, take the original bolt with you to a hardware store. The way to make sure the replacement you buy has the exact same pitch is to hold them side by side so the heads are on opposite ends, like this (sorry for the bad ascii):
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Then rotate the bolts inward against each other. Bolts with matching thread pitches will mesh exactly as they rotate and will stay in the same position relative to each other. In other words, they won't slide to the right or left as you rotate them.
