[suicideneil]

Very Small.

You'd need to grab some cheap 14mm or 17mm hexes from ebay or your LHS and have them measure the cross pin- I think they're about 1.5mm diameter but it varies- the hole can be slightly larger, doesnt have to be a tight fit as such. You'd also need to get the hole in the right spot along the stub-axle so that when the hex and wheel is fitted, it isnt hanging to far along or too close to the bearing that it might rub. That much is easy enough to work out once you have the parts to play with.