In order to understand how tubular rivets work, it is necessary to understand the difference between tubular rivets, semi-tubular rivets and normal rivets. Normal rivets are used to hold two materials together and are made of metal, designed to fit in pre-made holes and resemble smooth screws, lacking the ridges that give screws their torque. These solid rivets are placed in their holes, with the end opposite the head sticking slightly on the other side. This end is then hammered or bent into a flattened position, fastening the rivet there and forcing the two materials together.
The main problem with solid rivets is that they are restricted by length. If they are made too long, then their strength is compromised and any forced used to flatten to rivet into place may instead bend or break the rivet shaft, rendering it ineffective. If the rivet survives and is still too long, the objects it is fastening--often boards, metal sheets or similar materials--can bend or break it internally. To solve these problems, both the tubular and semi-tubular rivet were created.
These rivets are partially hollow. The end point of the rivet, which is typically flattened using a hammer or similar means, is instead left open, revealing the hollow inside of the rivet shaft, or shank. This makes the rivet shank look more like a hollow metal tube than anything else, but it is very important to note only part of the shank is hollow. The rest of the shaft, especially near the head, is solid and provides most of the support for the rivet. This means that the rivet resembles the solid construction from the head down until the shank reaches its hollow point, after which it resembles an empty metal tube.
The length of the hollow tube signifies whether the rivet is tubular or semi-tubular. According to the Orbitform Group, if the length of the hollow tube is less than 112 percent of the rivet body diameter, it is semi-tubular. If the length of the hollow portion is greater than 112 percent of the rive body, it is fully tubular. This makes a difference when the tubular rivet is set into place. Instead of using force to bend or flatten a solid end, force is instead applied instead the hollow tube. This causes the metal to give way, flaring out and rolling down until it meets the opposite side of the material from the head, locking down in a ring of pressure that holds the rivet in place.
Tubular rivets can theoretically be flared out and set by hand, but they are almost always set with a hand held rivet machine that inserts a plug into the hollow portion of the tube and automatically expands it and latches the bent shell to the surface. This requires only about half the force necessary for flattening a solid rivet, preserving rivet strength and saving energy. Semi tubular rivets generally offer stronger support than fully tubular rivets, but they both work in very similar manners.