any idea what this is or used for?

I hope you get an answer because we have one too and don’t know what it goes with. I thought it was part of a miter machine but don’t have enough pieces.
-Mike

Looks like a rule mitering device for shaving the end of lead rule to an angle and a precise length for making boxes or tables.

Bob

We call them Bolas , indeed it is for mitering rules and the like . Also used for whipping a little off the edge of a lead that needs less took off than you can get off with the lead and rule cutter . Very good and grazing the knuckle of the finger holding a small object ,when turning a quad into a triangle !!

Thanks for the help!

Yes it’s a mitering machine for cutting 45 degree angles at the end of rules - and because of the circular shaving action, it’s more precise than the more common downward-slicing Rouse miterers.