Great Planes ElectriFly 2.5:1 Elec Flight Gearbox FEATURES: Designed for electric airplanes using reverse rotation 550-size motors Converts the rotational speed from the motor to the propeller INCLUDES: One ElectriFly GD-600 Electric Flight Gear Drive 2.5:1 One 2.5:1 (18 tooth) steel pinion gear (GPMG0851) One precision machined aluminum pro REQUIRES: One ElectriFly T-600R Reverse Rotation Ferrite Motor (GPMG0705) OR a similar 550 size motor