What crafting item is this called?

It's a round on two sides and cylinder thing. It has a hole in it where I guess you can lace stuff through and I believe that it can be sown onto things, like corsets. It's basically what those things are that people have to put their shoe laces through to tie them but in my mind they look metal. Also what you do is stick one end on one side and the other on the other side of whatever you sow it to and then they fit together before you sow it to something.