Designed to be used with todays racing camshafts the register on the back of the hub is 1.950" with three .312" bolt mounting.
The three bolt design hub has a .250" dowel pin hole as well as massive .625" female hex to drive the fuel pump. Front of hub is set up for 1.00" I.D. thrust washer/bearing combos and all cam gear to hub bolts are tapped 5/16-24" thread.