Bits of Military kit that have no rhyme nor reason as to their functionality with a certain piece of kit. Flannelette is what we used to use. 4x2 whatever you want to call it.
The 4T/L42 scope was designed to take some stick and it certainly didn't need a very soft brush to clean it with nor a longer handled one if you didn't fancy the shorter one.
As I said earlier, a secondary thought by someone who never fired one, no more to it than that IMHO