RCD smooth 1pc. idler assm 3.25″ diam. where the belt rides, 4.375″ overall dia. and is 3.0″ wide. This pulley is made from billet alum. and has been hard black anodized for wear resistance. This pulley uses high speed precision bearings and is designed to be used with a .750″ bolt or stud and a 1″ t-nut.