Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number B57-13577-4 found under Large Diaphragm Ass by Raytheon Technical Services Company. The National Stock Number assigned to this part is 4420006504671, and the Federal Supply Class is . Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like B57-13577-4.