This is the Piston for the O.S. Engines 91HZ F3C Competition Helicopter Engine and the 91HZ-PS 3D PD-08 Pump Engine FEATURES: Aluminum construction Replaces worn or damaged pistons INCLUDES: One piston for the 91HZ F3C and 91HZ-PS Engines REQUIRES: Installation on the engine SPECS: Height: 25mm (0.98") Diameter: 27.6mm (1.08") cnh 11/11/08 ir/jxs