Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 3668216-503 found under Valve by Boeing Company The. The National Stock Number assigned to this part is 1660006244391, and the Federal Supply Class is 1660 Aircraft Air Conditioning Heating And Pressurizing Equipment. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 3668216-503.