Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number S1991M found under Die Set Rethreading Split Nut by Four Star Products Inc. The National Stock Number assigned to this part is 5136013553035, and the Federal Supply Class is 5136 Taps Dies And Collets Hand And Machine. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like S1991M.