This is the Extra Hard 5mm .8 Module 16 Tooth Brushless Motor Pinion Gear from Robinson Racing
FEATURES:
Will also work on stock motors using the a reducer sleeve (RRP1200)
INCLUDES:One 5mm .8 Module 16T Pinion GearOne 4x4mm set screw (RRP1201)
REQUIRES:Installation onto the motor shaft
SPECS:Length: 0.47" (12mm)Mounting hole diameter: 5mm