JayCee Cog pulleys for the Do it yourself race car builder. Made of 6061-billet aluminum. Upper pulley fits most aftermarket alternators with a .592" shaft. Lower pulley indexes off the stock pulley. (Must use a longer crank pulley bolt, P/N JC86250) Alternators can be driven 1 to 1 or under driven. Pulleys come hard anodized Black to prevent premature wear. Cog belt sold separately.