Use these engine sprockets to adjust the gear ratio on your jackshaft assembly. Sprockets use #35 chain. 5/8" bore size. See our gear ratio chart to determine which sizes will work best for your application. Choose from the following sizes 9t, 10t, 11t, 12t, 13t, 14t, 15t, 16t, 17t & 18t. The 9t, 10t and 11t sprockets have a built in key. The other sprockets require a 3/16" key sold separately. Set screws included.