Cheers for the link to the UK store. The main reason I was going for the 3 3/8th is because the mounts I'll be using combined with the 10mm HDPE base puts the centre of the shaft 37mm off the ground, which leaves the 2 7/8ths just too small to make contact with the ground (radius is approx 36.5mm). I would prefer a hex mount, but it seems that Banebots don't do any hex wheels above 2 7/8. Are there any other options for someone who doesn't have the equipment to make some?