Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number 137AY77-20 found under Filter Element Fluid by Watts Regulator Co. The National Stock Number assigned to this part is 4330000016310, and the Federal Supply Class is 4330 Centrifugals Separators And Pressure And Vacuum Filters. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like 137AY77-20.