Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number D-WK-563-21 PIECE 13 found under O Ring by Walz And Krenzer Inc. The National Stock Number assigned to this part is 5331011598381, and the Federal Supply Class is . Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like D-WK-563-21 PIECE 13.