A project I'm working on requires bicycle chain of specific lengths, master links are one way to make this happen but they cost money and banging the pins out and back in works fine and doesn't take much in the way of tools.

I had the idea to make very short chain loops to fiddle with, I find them pretty easy to put down but don't have much idle hand time these days.

Worn out bike chain can be had for free at most bike shops.