Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number K12-HMP-257 found under Valve Check by Trw Inc. The National Stock Number assigned to this part is 4820012349974, 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 K12-HMP-257.