Genuine GM govLock style posi for for all 7.625 or 7.5inch differentials with 28 spline axles. This is a 3 series Locker for gears from 3.23 - 4.56 and comes with 3.42 ring and pinion.It functions as an open differentials untill it senses one wheel slip and then it lock the axles together. For more info see Eatons web site. Fits all GM 7.5 differentials such as s10, camaro, firebird, cutlass, monte carlo, g body etc. This unit is in Very Nice condition. NO disappointments here. It can be purchased on ebay the item/auction # 120062546178.