JEGS Billet Alternator V-Belt Pulley provides 50% under drive allowing you to use it in high RPM applications and by slowing the alternator speed down it also frees up additional horsepower. The deep groove design insures that the belt stays on in high RPM applications. CNC machined from lightweight billet 6061-T6 aluminum to reduce the load on the alternator bearing. The 5" pulley is designed to be bolted onto and fit most GM and Ford style alternators. Requires a 36° x 17/32" wide v-belt. .