Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 551A found under Nut Tube Coupling by Lincoln Brass Works Inc. The National Stock Number assigned to this part is 4730000144307, and the Federal Supply Class is 4730 Hose Pipe Tube Lubrication And Railing Fittings. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 551A.