Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 173990 found under Spacer by Ontic Engineering And Mfg Inc. The National Stock Number assigned to this part is 5365000534535, and the Federal Supply Class is 5365 Bushings Rings Shims And Spacers. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 173990.