This is a new in the package Piston Ring set (1 set for each piston..so enough rings to do all 4 pistons) for all years and models:  1975 1976 1977 1978 Honda CB550K and CB550F Supersport Models models.   This is a standard size (STD) ring set.  #13011-374-000 This has the 2 compression rings and the lower oil control ring for all 4  pistons, everything to get your pistons/ engine running nicely again.   Get your old bike up and running again. We only sell the best! This is a top-quality aftermarket item shipped new in the package.