A sprocket comprises a sprocket portion having a plurality of radially extending teeth, a first coupling portion extending from a first side of the sprocket portion and having a first coupling structure disposed on an inner peripheral surface thereof, and a second coupling portion extending from an opposite second side of the sprocket portion and having a second coupling structure disposed on an outer peripheral surface thereof. In another embodiment of a sprocket according to the present invention, a sprocket comprises a sprocket portion having a plurality of radially extending teeth, a first coupling portion extending from a first side of the sprocket portion and having a first coupling structure disposed on an inner peripheral surface thereof, and a second coupling structure disposed on an inner peripheral surface of the sprocket.