I have just bought new wheels for my Raleigh mountain bike. Simple enough job changing over tubes and tyres and the freewheel. The front wheel sits in a treat as does the rear wheel until I try and tighten the wheel nuts, then the nut "rides" across the dropout. It is a new wheel, new axle and new nut so I all is true, and the previous wheel tightened without issue so I would have thought the frame was OK. To get round it I have put a washer between the wheelnut and the frame and that's OK. I have obviously lost the serrated nut edge against the frame, but years ago many bikes had smooth wheel nuts so shouldn't be a real problem. I may well try a couple of track nuts where the serrated washer is captive to the nut which can rotate separately to the washer. While typing this I have realised the one thing I haven't looked at is the actual nut. I will try the ones off the old wheel and see where it goes.