This is an OXY Heli Oxy 3 M0.5 Pinion Gear. The 11 and 14 tooth gears are included as stock equipment to provide a wide head speed range with both 3 and 4S batteries. 10, 12, 13 and 15 tooth gears are available to allow gear ratio options for various motor/battery combinations. Package includes one pinion gear and one set screw.
NOTE: Oxy Heli suggests that you do not exceed a head speed of 4500 RPM to maintain a compromise between performance and efficiency.