Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 4 40 UNRC X 25 found under Screw Cap Socket Head by H K Connecticut Holding Company. The National Stock Number assigned to this part is 5305012841379, 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 40 UNRC X 25.