Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 21C1-3-21 found under Pressure Switch Boo by Aar Parts Trading Inc. The National Stock Number assigned to this part is 1680015854813, and the Federal Supply Class is 1680 Miscellaneous Aircraft Accessories And Components. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 21C1-3-21.