A few sizes of circle dimple dies. I wasn't a big fan of what I was able to find so I made my own. These feature a hole through the center for a half inch bolt to be used if you don't have a press. If using that you will need some sort of backing plate. I used 1/4" steel plate for this as you will see in the pictures. These worked great with using an impact on a bolt on 16ga cold rolled steel. I have no idea what the limit is for how many can be done but so far I've been able to do 40 without the need to print another die set.

I printed these from carbon fiber nylon and have also done a set out of polycarbonate. You can do this from other materials if you please and with a little experimentation I'm sure you'll find that even PLA works just fine.

Currently I have only modeled 3 sizes. 1.5", 1.25" and 1". I may add more with time if I find myself needing more than these three sizes or if someone requests it.