This is a A-71872 Idler Sprocket PN: 71872Main Description As Following : A-71872 Idler Sprocket P.N: 71872 For No. 50 Chain (17 Tooth)Dim A (1): 5/8" BORE Stocked As: A-631905R91 Found in Section & Models : Miscellaneous > Miscellaneous, Farmhand (UNDEFINED): SEVERAL Associated Items : New Also This is An Aftermarket Product And : For No. 50 Chain (17 Tooth) Dim A (1): 5/8" BORE