These tubular 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.
In the world of fasteners, a tubular rivet is a great way to fasten two different pieces together. Rivets are mostly used when you are working with aluminum, thin metal, and even with plastics or leather. Rivets are made to mimic the look of smooth screws when they are set into the metal. Unlike screws, they are not easily taken out. You have to break off the rivets, or drill them out, in order to take the two pieces apart.
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.