Here is a picture of a Nano vs. 126T... In my hand the Nano seems smaller but is a little wider. If you could still insulate it you might make the 126T smaller by taking the wrap off. I have a page on my site here with dimensions of about all the smaller decoders I could find... http://1fatgmc.com/RailRoad/Decoder-1/page-3.html I don't have a Micro and it looks to be a touch smaller than the Nano but maybe not enough to count. Without the loco in hand it is hard to recommend one. I'd get both and see which might be the better choice and use the other one in another install which I bet you end up doing sooner vs. later . I have two of the Nano's on hand if I need them but so far haven't installed one as they are more expensive so probably will only use them when absolutely necessary. I have installed some of the 126T's but if I can fit it use the 123's as they are less expensive and that is a consideration for me. Sumner
Found the original manual for this: https://www.nsesoftware.nl/vdweerdt_nl/manuals/arnold/arnold_2055_a.html The object in the original question is a "scheibenkondensator"; in plain English a disc capacitor. Capacitors and coils can be removed when converting to DCC. Kuehn, Zimo and several other "European" Decoder manufacturers have small and very capable nano and microdecoders. Main thing to worry about is te max load of the motor vs the max load of the decoder (obviously).
