Not 100% sure. I have only dealt with Nimrod parts on a small basis and never seen a Parts Catalogue…. and I have never dealt with Comet parts. I would have to say that I would assume that 6M would be Nimrod only although I am pretty sure that there probably would have been some cross referal both ways. The number breaks right down from aircraft type, series, where it goes on the airframe to the “individual part number”. In this case 6M 4 EC. It is by no means an exact science. With access to a parts catalogue someone could tell you probably what it is, where it goes and how many are on the aircraft within the space of a minute, and perhaps provide a pretty picture as well. I would be able to give a list of the part number letter codes in an hour or so.

The 6 is the deHavilland Comet and Comet related parts. Bruce may well know more.There is a list on this very forum (somewhere) but it is, of course, by no means complete. I deal a lot with aircraft parts as my business and I am always learning when I have in new stuff, and a lot of it stays in my head… bit sad really – I can remember crap like this but have a problem with my familys birthdays although I have never forgotten my wedding anniversay but the wife has!!