This is an excellent plastic worm gear. Use it to get your motor to run at the desired speed and torque. Worm gears, in conjunction with pinion or spur gears, are used to change the rotational plane by 90 degrees. It has a 6mm bore and a set screw, making it simple to attach the gear to various diameter motors and axles. Ideal for use in science projects, robotics, and so on.