At some point more than likely the rotors got into this back bearing plate and looks like someone machined the plate flat and glued a .035" sheet of Teflon to bring the clearances back into spec. From the Teflon surface to where the bearing plate seals against the case it measures .755". Rear bearing plate will work with older B, C or D rotor blowers. Typically going to be all serial numbers lower than #1000.
Plate looks like it was run after the Teflon was installed as there is Teflon strip wear marks in the rear plate Teflon.
Note: This is a used item. This item might have been taken in on a trade. RBS may have inspected this item and deemed re-usable. There is no warranty expressed or implied with this item.