Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 7731S found under Respirator Air Filtering by Siebe North Inc. The National Stock Number assigned to this part is 4240012499263, and the Federal Supply Class is 4240 Safety And Rescue Equipment. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 7731S.