Thanks man, that sounds interesting.
I will check that in the garage in a sec before I leave to go buy some tools. I measured the hole and it seems to be a 12mm and my largest allen is a 10mm (except the wheel tool I got which is 17 up to 22). It seems right too as the 10mm is way closer to the size than the 17mm.
While I was at it I took the caliper and measured the rear wheel nut and that seesm to be a 24mm socket (not allen) and as that has a lot of torque I will try to find a 6 sided.
Dave