This is the Piston for use on the O.S. 55HZ-H Hyper Ringed Engine (OSMG1955). FEATURES: Aluminum construction Silver in color INCLUDES: One Piston REQUIRES: Installation in cylinder liner SPECS: Length: 21.7mm (0.85") Diameter: 22.9mm (0.90") cnh 11/5/09 ir/jxs