How to Size a Rivet’s Length

A rivet has to do two jobs at once: pass through every layer of material (the grip) and leave enough tail sticking out the back to be hammered or pressed into a second head. Too short and there is nothing to form the head; too long and the shank buckles sideways instead of upsetting cleanly. The working rule is simple:

where the grip is the combined thickness of all the layers and k is the tail allowance — about 1.5 for a solid rivet. Round the answer up to the next size your supplier stocks.

Solid, Semi-Tubular and Tubular Rivets

How much tail you need depends on how the second head forms. A solid rivet upsets entirely from its own shank, so it wants the most tail (k around 1.5). A semi-tubular rivet has a partial hole that lets the end roll outward with less material (k around 1.0). A tubular rivet rolls over even more easily and needs the least (k around 0.7). Blind (pop) rivets are different again — they are chosen by grip range rather than cut to length.

Why Grip-to-Diameter Matters

The healthiest rivets have a grip between one and three times their diameter. Below that and a thin sheet can let the head pull through; above it and the long unsupported shank tends to bend before it fills the hole. If your grip pushes past 3d, step up to a larger diameter or spread the load over more rivets rather than reaching for a longer one.