These are nail punches. I'm not all that sure what they're supposed to be for but they work great with riveting. They can hold the rivet top when it's in a hard place to reach. The end of the tool can be hammered on. This is what I did with my cuff bracelet: I used it on the rivet top while hammering the back of the rivet when the rivet was in a recessed area. One of the best things about them is that the end of the tool is cupped. This keeps the front side of domed rivets from being flattened during the riveting process. There's still a little deformation, but not what you get by putting the rivet head on your bench block.
Nail punches can also be used as a decorative circle stamp.
They come singly or in sets of three, with different sized ends. They are widely available. I think I paid about 10 dollars for for the set of three Kobalts pictured above, but you can get very inexpensive sets like this one I saw at KC Tools.
