I found a pair of these among some parts I bought. It looks like some sort of cylinder, which could hold an axle for a piston.
Is that correct, and how would I use it then?
This, at least as far as my experience goes, is used simply to create extra friction in joints; to make something poseable yet stiff and able to hold its position. Sorry no pic, but a good example is the 8996 Scorpio XV1, a walking machine that uses these to keep the legs stationary unless you actually want to move them.