This listing is for a sprocket. Make: Martin Model / Part #: 41BTB18 Description: Single Taper Bushed Sprocket Includes all/only items pictured. Here is some information from the manufacturer... Single Taper Bushed No. Teeth: 18 Catalog Number: 41BTB18 Bushing: 1210 Diameters Outside Diameter: 3.14 Pitch Diameter: 2.879 Max Bore: 1 1/4 Dimensions (L): 1 Dimensions (C): 2 3/8 Type: B Martin's online product page is located at http://www.martinsprocket.com/Sece/no41.htm