This is the Master Airscrew 13x8 3-Blade Pusher Propeller. FEATURES: Constructed of glass filled nylon for strength and durability NACA airfoil Scale look and true pitch Accurately balanced to create a greater thrust at lower RPM SPECS: Diameter: 13" (33cm) Pitch: 8" (20cm) COMMENTS: The general rule for converting a 2 blade prop to a 3 blade is to subtract 1" from Diameter OR subtract 1 from Pitch. Pusher propellers are designed for airplanes that have the engine facing backwards in the rear of the plane, PUSHING the airplane forward. PER MASTER AIRSCREW: All 3- and 4-blade props are balanced dynamically at the factory prior to drilling. The mounting holes are then drilled slightly off center, if required, to properly balance the propeller. As such, the mounting hole may be slightly off center. Master Airscrew assures us this is perfectly normal and will not cause problems during use. jxs 9/09/08 ir/jxs