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Apart from the $300 Leica service, one way to get lenses coded is to replace the flange, or send it away for coding to a third party. This led me to do some research on flanges. There is a Chinese vendor offering what I call Type I flanges, and also Type II ones. Here is what I found out. Note that:- All measurements in degrees clockwise from the centre of the key as viewed looking at the rear of the lens. Measurement are approximate and have been rounded to what appears to be the nearest whole number. All flanges come in three variations for 28/90, 50/75, or 24/35 viwefinder frame lines. 6-bit code start 115 finish 142 Type I flanges These appear to be on all digital era lenses as the screws don't invade the code area. Six screws at 40 80 160 210 275 340 Type II flanges Examples I have seen include Product Year 11815 1982 Summilux 75mm f/1.4 11800 1973 Tele-Elmarit 90mm f/2.8 11134 1991 Elmarit 21mm f/2.8 Six screws at 60 72 36 72 72 36 Note that the second screw sits right in the 6-bit code area and looks like a "1" to the sensor. Thus uncoded lens with type II flange looks to have code 000100. Which is great if it is the 90mm above, but a problem elsewhere. Type III flanges I have only seen one. Product Year 11817 1968 Summicron II 50mm f/2.0 Five screws at 45 135 225 270 315 Again, the second screw sits right in the 6-bit code area and looks like a "1" to the sensor. Worse though, if that screw is omitted, there will be a full 180 degrees without one. I'm not sure if the flange would stay flat and square under such circumstances. Type O flanges I call them this as they have no screws at all in the face of the flange This makes it difficult to remove. I think all the early lenses were made like this Examples are Product Year 11631 1955 Elmar 90mm f/4.0 11870 1967 Summilux 35mm f/1.4 - (this has screws around the edge of the flange) 11118 1953 Summicron (I) 50mm f/2.0 11850 1961 Elmar 135mm f/4.0 16464 OTZFO M-mount for Visoflex lens heads also the Voigtlander 12mm Ultra-Wide Heliar (are all Voigt. flanges screw-free?) I hope this helps.