I am not near my tools now to measure, and don't remember what size the punch is, but the important thing I think is that the rivets can be pushed through the hole the punch makes by hand. They should be snug, but not too tight. The width and thickness of biothane depends on the dog handlers preference. I have made them as thin as 3/8 inch and as wide at 1 inch. When choosing rivet length, Please consider the total thickness of biothane you will have to go through. for example if you will be folding the biothane back as in the video that will be 2 layers thick and you will need a rivet that exceeds that by a margin large enough to mushroom the rivet over the top of the washer.

Rivets: tandyleather.com/collections/hardware/products/rivets-burrs?variant=31978061168771 Rivet Burr Setter: tandyleather.com/collections/tools/products/craftool-copper-brass-rivet-burr-setters Rivet Plate (only needed if you don't have an anvil or other hard metal surface to pound on): tandyleather.com/collections/tools/products/deluxe-snaprivet-plate Note: The rivets and setter have to be the same size if you get #12 rivets you will need the #12 setter. I get my rivets longer than I need, for example 1 inch long, because I can always cut them off shorter but if all i have is short rivets and I need a longer one I have to go shopping. I hope this helps, have fun making you leashes!