Back cover for 6.5 and 7.5 rear intake with disc type valve.
This one uses a set screw to retain the rotor pin.
K&B made several style rear intake back covers.
Check yours, this has a diameter of 1.125" and protrudes into the case .495" and fits a carb neck diameter of .437". This is for use with the steel disk and hardened steel pin.
This is the later version, the earlier version was hard chrome plated and used an aluminum disk. It did not have a set screw, the pin was pressed in.