Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number PSM4B40-4 found under Washer Flat by Barnett Instrument Co. The National Stock Number assigned to this part is 5310005618419, and the Federal Supply Class is 5310 Nuts And Washers. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like PSM4B40-4.