Geoff Stenner
A bit late to the show, but please remember EM standards (Denny, Pendon etc.) were originally 18mm gauge. The extra .2mm was added when Stephen Poole wheels appeared in the ’70s, when we all had to use only Hamblings (see Guy Williams first book) or Romfords and the Poole wheels were a useful alternative. The latter had thick flanges and are long defunct and meanwhile, proprietary wheel standards have improved hugely so along with that and the fine standards of wheels from Gibson and Ultrascale, I doubt that he extra .2mm is needed in the 21st century. Sharman standard wheels worked ok in P4, too, and were revolutionary with their fine profile when they first appeared, so another example of the redundancy of the extra gauge.