This is a Great Planes ElectriFly 4.0mm - 1/4-28 Prop Drive (adapter) with Set Screw and Prop Nut. FEATURES: Mounts onto the shaft coming out of a gearbox or motor with the included set screw. The propeller mounts onto this with the included nut Aluminum prop drive Metal hardware One year quality guarantee. Fits a 4mm motor shaft with a 1/4" prop shaft. INCLUDES: One Prop Drive One 3.5x5mm Set Screw One 7/16 Propeller Nut REQUIRES: Installation onto the motor or gearbox shaft. SPECS: Length: 1.5" (37mm) end to end .98" (25mm) complete shaft w/.69" (17.6mm) threaded portion. Diameter: 1/46" (6.27mm) prop shaft .16" (4mm) ID for motor shaft .78" (20mm) largest part of hub (thrust washer portion) .47" (12mm) smallest part of hub rmb 12-05-06 ir/jxs