This part should always be replaced when installing a new clutch disk. Even if the old one "looks good", wear patterns have been established and the replacement disk will wear out prematurely if it's re-used.
Replaces BMW Part Number 21 21 1 251 801
Always also replace the diaphragm spring, compression Ring and 6 bolts. Fits all models from /5 to 09/80 production except R45/65