Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 999-6520-A-003 REV B ITEM 89K found under O Ring by Carver Supply Inc. The National Stock Number assigned to this part is 5331015867516, 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 999-6520-A-003 REV B ITEM 89K.