This is a A-18311-018SW Spring PN: 18311-018SWMain Description As Following : A-18311-018SW Spring P.N: 18311-018SW A-18311-018SW Spring P.N: 18311-018SW Stocked As: A-80A80 , Crossed From: SW02132 , Found in Section & Models : Hay Tool Parts > Slip Clutch Parts, Sidewinder ROTARY CUTTER: SEVERAL Associated Items : New Also This is An Aftermarket Product And : Inside Diameter: 2.88" Outside Diameter: 4.725"