THIS IS A STEEL REPLACEMENT PULLEY FOR THE LS1 MOTOR IN CAMARO SS, Z28, FIREBIRD FORMULA, TRANS AM WS6; WITH ORIGINAL FACTORY PLASTIC PART# 12559885. THIS PULLEY WILL STOP THE NEED OF REPLACEMENT EVERY TIME THE PLASTIC BREAKS, OR COMES APART, AND RUINS THE PUMP RESERVOIR, AND LOSES THE BELT. ALLOWS FOR EASY ACCESS TO THE PUMP BOLTS SO THE PULLEY DOES NOT HAVE TO BE REMOVED TO GET THE PUMP OFF! GUARANTEED TO FIT 98-02 LS1 MOTORS AND REPLACE THE PLASTIC PART# 12559885. EXACT OVERALL DIMENSIONS AS THE OEM PART. OUTSIDE DIAMETER IS 6.6 INCHES AND 6.469in @ BELT GROOVE; BORE IS 0.7472 INCHES OR 18.9789mm TO FIT 19mm/.75in SHAFT SIZE (SAME OFFSET AS FACTORY PART) SIMPLY PRESS ON UNTIL THE BELT DRIVE IS PERFECTLY ALIGNEDDOUBLE CHECK ALIGNMENT WITH BELT AND ACCESSORIES(ALTERNATOR, CRANK SHAFT, ETC.) FOR CORRECT PLACEMENT. There will be about 1/4'' of the bore not pressed on the shaft, because the factory part has a 1/4'' 'lip' inside it to make it 'stop' when it is aligned. These are made with no 'stop' inside. My plastic part broke at the center shaft while on the expressway, and busted the reservoir, losing the serpentine belt, and leaving me stranded miles from nowhere. It came apart at 107,000mi. I also saw one on youtube explode during a dyno test and ruin the radiator hose and the radiator. It is very expensive when the plastic fails! DON'T WAIT UNTIL THIS HAPPENS!Get one now to be on the safe side.I HAVE SOLD A LOT OF THESE TO VERY SATISFIED CUSTOMERS.THIS IS THE BEST REPLACEMENT PART FOR THOSE PLASTIC COMPOSITE PULLEYS. IT WILL LAST THE LIFE OF THE CAR.If you need any assistance with the install, feel free to message me. I have 30+ years experience as a mechanic and will help whenever I can.