Here is a photo of the current setup:
http://upload.pbase.com/image/125406721
The axle is an M10 bolt with a domed head. It isn't a proper fit in the wheel which seems to need something like an M12 or 14. The wheel itslef is wider than I would like as the C purlin only has 45mm of clear space. The dome head bolt end has a little squared off section as it is designed to bolt timber together. The wheel has roller bearings.
Chris how do prevent the roof from blowing off in heavy winds?
Some sort of lockdown system?
Greg.