Brent, As you can tell, it's called a "Univise." These have multiple degrees of freedom and are used in grinding or light milling to present the work at a complex angle. Reliable Tools recently sold one on eBay for $200 or so -- more than it's worth as a compound angle vise IMO. Still, lots of Rockwell/Delta Toolmaker grinder and mill owners like to add them to their kit. Sounds like you own the mill -- keep it.