I’m not certain which British WWII Military Aircraft this item fits. The box markings identify it as “Socket 2 Way Switch Type 5c/859”. It has the “A” “British Crown” “M” and “REF. No. 5c/859” in raised letters on it as can be seen in the photos. It is 3-1/4” diameter and 1-7/16” deep body plus three studs extended 3/4" beyond the body depth. It is a 2 part spring loaded body. You twist the top part to the right and it exposes the 2 brass contact holes: one is .315 inches (8 mm) diameter and the other .375 inches (9.5 mm) diameter.  On the back, it has three threaded studs for wiring: one is marked “B+” another is “B-“ and the third is marked “M2”. It also has 3 each brass threaded inserts for mounting the unit. My guess is that it being spring loaded, it keeps the electrical contacts from being exposed when not being used.

If anyone knows which British aircraft this fits, it will be greatly appreciated as then I can identify it correctly.