Punch and die sets. I have 2 from Waldron, 1 from micro mark, and 1 I made myself which lets me punch a variety of different diameter discs in plastic sheet, light brass or aluminum, decal sheets, etc.
There are a lot of different ones out there now. UMM-USA & RP Toolz are a couple I can think of off the top of my head. They are not cheap, but they are indispensable for scratchbuilding, in my opinion.
29. April, 13:05