Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number CSR503-1 found under Retainer Fastener Auxiliary by Emhart Industries Inc. The National Stock Number assigned to this part is 5325004255013, and the Federal Supply Class is 5325 Fastening Devices. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like CSR503-1.