This O-Ring secures one of the brake pad to the piston of the caliper. The other brake pad is secured by a spring clip (part number 3411513 ) When replacing the brake pads, it's a very good idea to also replace this o-ring. One o-ring is needed per caliper. If you bike has dual disks, order two o-rings.
For all ATE brake calipers; 1974 through 1980 model years.
Equivalent to BMW Part Number 34 11 1 233 120