Bought it; how do I use it?

[Vinny]

It looks like it's for knurling the end of a piece of metal without having to center drill it. You'll have to figure out what size to turn the metal to so the knurls line up, then put it over your piece of metal and tighten the 3 screws. Oil it up and start knurling. But don't take my word for it, I've never even seen one of them!