Yesterday I helped clear out an old DIYer's workshop and found a plug I couldn't make sense of. It's a rather small angle plug (small by European standards), the face is about 3.5 cm square. The 4 round pins are very thin, only around 2 mm and maybe 10 mm long. There are hardly any markings, but the screw terminals inside are marked R, Y, GN, BK. The only interpretation that comes to my mind is red, yellow, green and black, which sounds like phone wiring. The screws look decidedly un-metric, or if they are, the number of threads is non-standard (coarser than the average M3). If plugged in with the cable exiting at the bottom, the top pins are spaced closer together than the bottom ones, i.e. the plug is polarised.
Any ideas what that could be? I can take pictures and exact measurements later.