Really appreciate all the research! I also wondered if it was used on other NF w/solid nose types, but didn't find anything. But, now, going by the photos showing it, fitted to Ju 88s with a glazed nose, stops one idea. Had in mind maybe a oxygen pressure regulator for the air-operated firing system, for the MG FF. The photo I'm going by, as I'm sure many of you know, is written as an early C series. What I've read on that is, the C-1 was the first prototype, the C-2 first to be 'produced', C-3 the next prototype, and so on. And, I'll add the C-2 was built, using high-time A-1 airframes, with the shorter wings. Anyway, thanks! Gives me more to search for.