The T-2, M48 and M68 connection system are threaded methods of connecting many cameras, filter wheels and other accessories together.
There may be some occasions when you connect items together and find that either one item is rotated “too far” (e.g. camera is just at the wrong angle) or you may need just an extra little bit of distance between your reducer and camera to get the spacing correct.
Baader offer a useful set of aluminium fine adjustment rings that are available in the popular T-2 size as well as M48 and M68 sizes too. These rings are available in 0.3mm, 0.5mm and 1mm thickness. The 0.3mm thickness variant corresponds to approximately 2/5th of a full turn, with the 0.5mm and 1mm thickness models corresponding to ~2/3 and ~1+1/3 of a turn respectively. To help identify the rings and their thickness Baader have colour-coded them. These rings can also be used for eyepiece projection adjustments and also prevent binding between the two components used.