Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 21-18 found under Blade Windshield Wiper by Electro Switch Corp. The National Stock Number assigned to this part is 2540000815441, and the Federal Supply Class is 2540 Vehicular Furniture And Accessories. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 21-18.