Serpentine Pulley Kits Facilitate the use of high power Alternators Better Power Transfer Reduced Vibration and Belt Dust Quieter Motoring Single Vee pulleys can only support alternator power loads (PTO) of up to 100A for 12V applications (45A for 24V applications). A serpentine pulley provides greater surface contact between the belt and pulley, and thus can accommodate much higher PTO requirements. Westerbeke Engines Covered: 21, 13A, 27 Kit Includes: Three Ten-Groove (J10) Pulleys, Two J10, 40″ Circumference Serpentine Belt & Mounting Hardware PLUS not shown 2 extra alternator pulleys