Ofna hop-up has high quality N66 nylon gear with changable all aluminium parts made by a CNC lather machine. The gear ratio is tuned to optional engine use, and other gears are also available for changing the gear ratio. This unit also has adjustable gear shift timing. This kit includes 43T spur gear (blue), 2 5x10 ball bearings, 39T spur gear (yellow), 1st gear carrier, 2nd gear carrier, clutch cam, clutch bell, 15t clutch gear, 19T clutch gear, main shaft and instructions.