Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 639543-401 found under Lockspring Turnlock Fastener by Bae Systems Information And Electronic Systems Integration Inc Div Bae Systems. The National Stock Number assigned to this part is 5325002853373, and the Federal Supply Class is 5325 Fastening Devices. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 639543-401.