This is the Cylinder Liner for the O.S. 91HZ F3C Competition Helicopter Engine and the O.S. 91HZ-PS 3D PD-08 Pump FEATURES: 5-ports cut in Constructed of steel INCLUDES: One Cylinder liner SPECS: Height: 45mm (1.77") Outside Diameter: 31mm (1.2") Inside Diameter (bore): 27.65mm (1.09") REQUIRES: Installation into the OS .91HZ-PS or the O.S. .91HZ F3C cnh 11/5/08 ir/jxs