Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 21-3717 found under Sleeve Valve by Acf Industries Inc. The National Stock Number assigned to this part is 2240004135294, and the Federal Supply Class is 2240 Locomotive And Rail Car Accessories And Components. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 21-3717.