I’m fitting new bath and basin taps for a friend. Bath ones were fine but when I came to take off the basin ones my 27mm box spanner is too big for the back nut. It’s hard to measure up there but looks perhaps between 22 and 24mm. Just wondered if anyone knew of other standard size back nuts smaller than the 27mm AF size or is it a case of me having to buy a set of box spanners and seeing which one fit. Actually the bath ones were a bit of a pain as the tap connector nut (not the back nut) was between the 27mm and 32mm sizes of my basin wrench so had to fiddle around with an adjustable spanner up there. They were Yorkshire tap connectors not flexi ones. I was surprised that the wrench didn’t fit as i thought that is what they are for. Cheers James.