This is a A-745023 Idler Sprocket PN: 745023Main Description As Following : A-745023 Idler Sprocket P.N: 745023 For No. 550 & 555 Corn Header Chain (8-Tooth)Dim A (1): 5/8" BORE Stocked As: A-AN102448 , Crosses To: A-AN102448 , Found in Section & Models : Miscellaneous > Miscellaneous, New Idea (UNDEFINED): SEVERAL Associated Items : New Also This is An Aftermarket Product And : For No. 550 & 555 Corn Header Chain (8-Tooth) Dim A (1): 5/8" BORE