i get a few ppl asking about rivets, and there are a few ways to make them by hand. this is the first step in this method, with this type of tool, which clamps the material to allow upsetting the rod to create the bulk for the head of the rivet. from here it goes to the header plate and a heading (shaper tool) tool shapes the rivet head. (other video for part 2, the head)
(the three ways are,(1) upset, make larger, the material to form a head, from the shaft size material. (2) reduce from larger stock to form the shaft, leaving the bulk for the head. (3) buy them !........lol ..or..you can forge weld a collar, as for making a bolt/rivet, adding bulk for the head, using heat, hammer and anvil.