Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 4-40UNCX1 4 found under Screw Cap Socket Head by Unbrako A Division Of S P S Technolo. The National Stock Number assigned to this part is 5305000800064, 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 4-40UNCX1 4.