35mm everytime. So a customers says they are having standard white fittings, you say so you are definately not having flate plate or dimmers etc and they say no
so you 1st fix with 25mm, plastering is done and then come to second fix and the customer has changed their minds and has bought some flate plate etc. You then explain the difficulty and that they said they were not having flate plate, but it dont matter, they think you are the bad guy. I had this once when I was subbing for another spark, fortunately learnt this one without it costing me any time/money
Save the hassle and fit 35mm at first fix stage!