Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 237 21 found under Packing Nut by Nav Aids Ltd. The National Stock Number assigned to this part is 4730219122002, 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 237 21.