Reproduction Honda CB500K and CB550 cam chain slipper which was also used on the '75 CB360T. As your engine runs the cam chain is spinning all the time and it slowly wears all of the parts that guide it and put tension on it. If you're doing your top end and you plan to replace the cam chain and it's associated parts, it's a good idea. Check for wear of course, but sometimes it's good to go by the "while you're in there" approach.
The slipper is on the back side of the engine, closer to the carbs.
Replaces Honda OEM Part Number: 14520-323-000
Fits Honda:
CB360T - 1975
CB500K Four - 1971-1973
CB550K Four - 1974-1978
CB550F Super Sport - 1975-1977