Chevy polished aluminum billet 6 groove serpentine crank and Alternator pulleys set. These are for the Chevy Set includes crank and alternator pulleys only. Recommended for automatic transmission vehicles. 1988-1992 305-350 Camaro, Firebird, Caprice engine. The pulleys are CNC-machined from the lightest, most durable materials possible; 6061-T6 aluminum billet and polished to a near mirror finish. The crank pulley are in 6 7/8" diameter. The Alternator pulley are in 1 7/8" diameter.