Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number ESR904 found under 4 Port Serial Aircr by B And B Electronics Mfg Co. The National Stock Number assigned to this part is 5999015840531, and the Federal Supply Class is 5999 Miscellaneous Electrical And Electronic Components. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like ESR904.