It is a commonly used mechanism for producing an intermittent rotary motion from a uniform input speed.

The driven member, or star wheel, contains evenly spaced slots into which the roller of the driving crank slides into. As the drive wheel turns it enter the slots of the driven, or star, wheel and the mechanism enter its motion period. As the pin leaves the slot the drive wheel has been indexed and it continues to stay stationary until the pin rotates back around.