Fastener center

Fastener Size Reference

Thread size, fastener length, head dimensions and strength grade are separate pieces of information. This reference helps keep them separate.

Reference library

Focused pages with a clear owner

Each URL answers a distinct question. ThreadSizeGuide avoids automatically generating thin pages for every possible size.

Learn how inch and metric bolt size callouts encode nominal diameter, thread pitch or TPI, and length.

Understand how head style and fastener specification determine wrench size independently of thread diameter.