My mother collared me the other day with a request to fix a toilet roll holder. At first I couldn't see anything wrong, but eventually found that a grubscrew is missing. This grubscrew centralises a chrome flap which half covers the toilet roll and, I think, provides the user with a flat edge to tear the serated sheets off against IYSWIM. The strange thing is, the thread does not conform to UNC, UNF or metric pitching. Fortunately, the grubscrew that retains the holder onto its wall bracket is the same thread, so this can be examined closely.
Are these fittings renowned for using odd-ball thread types? The toilet roll holder was part of a refurb job, so unfortunately maker's details are not known.