Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number AC4257-A found under Cock Drain by F M C Corp. The National Stock Number assigned to this part is 4820000268473, and the Federal Supply Class is 4820 Valves Nonpowered. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like AC4257-A.