Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 303-B found under Retainer Disk Valve by Ruthman Pump And Engineering Inc. The National Stock Number assigned to this part is 4820014204995, and the Federal Supply Class is 4820 Valves Nonpowered. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 303-B.