Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 173 187 R91 found under Ring Set Piston by Navistar Intl Corp. The National Stock Number assigned to this part is 2805000755508, and the Federal Supply Class is 2805 Gasoline Reciprocating Engines Except Aircraft And Components. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 173 187 R91.