So there are two little parts do NOT show up on any parts fiche blow up I can find, nor are they mentioned in the service manual...
But one of them is DEFINITELY THERE in one of the photos in the service manual.
I picked up a barn fresh 77 cb750f with only 6k original miles and it was fully stock. The original tires, pads, everything were on it like a time capsule.
Only one of the front calipers had this part on it... So???
My guess is these are in place to create a low-friction platform allowing the pads to easily slip back and forth as the piston comes out and retracts, as opposed to hanging up on the rough surface of the cast caliper. I have no idea why there is no part number for them. Do you?