Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number SS21MK21TEM37 found under Screw Cap Socket He by G E C Marconi Avionics Ltd. The National Stock Number assigned to this part is 5305991366055, and the Federal Supply Class is 5305 Screws. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like SS21MK21TEM37.