Actually, belt clipper tools. Flat leather belts or the rubbery black ones from TSC work the same. There are at least 4 different tools and ways. I'm not even going to beveled edges, glue and lacing now. The number is 6 for smaller flat belts of around 1-2" . Then put a pin and go. I probably should have mentioned 20 years ago that the best clippers were supported in a light cardboard fixture. It was spaced to fit the clippers into the machine. These cardboard could break or rot away so the individual clips were placed individually. It may look like a rotted mess on the floor but they fit a tool which I call a machine. These are not alligator clips where you pound on them.
The tool/machine, came in different sizes for there is grip, location , proper clip size and lock it down. Compression by levers or near a screw press. The die foot shapes the ends to curl around into the belting.
These are cool things along with the clips for as long as we have flat belts.