Rear motorcycle sprocket RR521 by Ryno. This is the sprocket located on the rear wheel of the motorcycle. It is also called the "large sprocket" and is usually larger in diameter than the front sprocket. The one part of the chain is "attached" to the large sprocket, through which the movement is transferred from the engine.

It has 36 teeth, which means that it has this specific number of teeth on its perimeter. The pitch of the chain, which is 420, is the distance between its pins. This is indicated by the first digit of the above number, while the other two digits refer to the width and strength of the chain.