This is a microwave turntable drive motor. It accepts a D-shaped drive shaft. The drive motor is located under the glass microwave turntable, and allows the turntable plate to rotate while the appliance is in use. Your drive motor might be broken if it is noisy or does not turn at all. Be sure to disconnect power to the microwave before starting this repair.

Turntable Motor
21V AC, 50/60Hz, 2.5/3 RPM, 3.0W with D shaft.