I'm building a WD M20 gearbox, the shell's filler spout thread has a 5/8" BSP thread, The usual thread size for this filler plug is 1/2" BSP. Funnily enough I have the correct filler plug in my box of gearbox spares, it doesn't have the "keep full" stamped on it but the piled arms. Does anyone know when this larger plug was used? It might be late war as the part number is unreadable. Neale?
