It's a couple three inches tall. I think I inherited it from one of my dad's odds and ends boxes. 

I'm guessing a chain breaker. Maybe for bicycle chain

NEAL IS RIGHT IT PRESSES THE PINS IN A CHAIN    bobw.

Agreed. And it is invaluable when you need one.

Makes sense. Funny thing is, many, many years ago I worked in a farm store and took apart more than a few master links, but I'll be damned if I remember how it was done or what tool was used. I guess that bit of knowledge got crowded out of the ol' brain over the years. I don't think we had one of those though. Thanks guys.

You probably had the ones with C clips, all you need is pliers...;P

I havent seen one of those in many years and it brings back fond memories, thanks