I measured the tubes and they seem to be metric dimensions, top tube was 26mm, the seat tube 29.8 more or less, although verging on higher and the down tube was bang on 29mm. I also measured the seat tube inner diameter with the bolt removed and got 26.6 but I assume if there had been a too small seatpost in there for a while it would need some opening up to get back into shape. Also tried a 27.2mm seatpost which was definitely not going to fit.