The everyday case — a hex, round, pan, or button head that sits on top of the surface. Length is the one to get right.
This covers any fastener whose head sits on top of the material — hex cap screws (what most people call “hex bolts”), plus round, pan, truss, and button heads. The head rests above the surface, so it doesn’t count toward length.
Measure from under the head to the tip. The head sits on top of the surface, so it isn’t part of the length.
Picture the bolt installed: the head sits on the surface and everything below it goes into the joint. The part that actually does the work — what passes through and grips — is everything under the head. That’s why length is taken from there, and it’s why two bolts with the same length can have different-sized heads without changing the measurement.
Rule of thumb: whatever ends up buried in the joint is the length. For these heads, that’s everything below the head.
Those two don’t change with head type — diameter across the shank, thread by counting threads per inch. If you need a refresher on either, it’s on the measuring basics page, along with a printable ruler.
If your fastener sinks flush or has no head, length is measured differently. Jump to the right guide — or bring it in and we’ll size it.
