Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number D5559-21 found under Fitting Lubrication by P J Valves Inc. The National Stock Number assigned to this part is 4730013997423, 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 D5559-21.