Ksor,
Yes as Bill has already pointed out, That's a universal dividing head. Heads like that should come with about 12 different gears and a type of banjo much like a plain change gear lathes banjo. It's designed to be mounted on the end of your mills table and this allows you to set up various combinations of gear trains to allow the proper head rotation verses the amount of distance the table travels in the X axis. I know less than nothing about your exact mill type, But it's possible you'll see a area machined away on your mills X axis leadscrew bearing hanger to allow different gears to be fixed to the end of the leadscrew. The whole system works much like a gear train set up for cutting threads on a lathe. But very long leads, Or to use a thread cutting term, Very low thread counts per inch. You could for example have one complete thread revolution over 12", And even make it a multi start thread using the dividing head. If I was far more competent with computers I'd find and post some direct links for you about how these heads get set up and used.
Pete