1 groove water pump pulley and bolts. Bolt circle for water pump pulley is 2-1/4" with a 5/8" pilot hole. Water pump pulley is 6-5/8 in diameter. Crank pulley is 6-5/8 in diameter. It's a great option if you running power steering and NO A/C.It Will not work with Vortec engines. Will not work with reverse rotation pumps.