This is the large pilot bushing in the back of the crankshaft. This bushing is a roller vs the smaller bronze of the early motors. It is  important to make sure the rollers are not pitted. These are found in the later 1275cc motors. Check for a good fit in crank. You do not want a sloppy fit. If sloppy the 1st motion shaft will wobble thus causing the trans front cover scrolls to wear. It sure helps to use our front cover with a seal installed. See part #RCT-429.
The size of this bushing is .750 OD.