Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number X21-504-18 found under Gasket by Bofors A B. The National Stock Number assigned to this part is 5330008074773, and the Federal Supply Class is 5330 Packing And Gasket Materials. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like X21-504-18.