Loctite??? ye gods!This is all very helpful. I have a friend's "Hall" here which had one driver where the screw had come out and jammed the coupling rods. Easily fixed. But on the opposite wheel I suspect the screw has been Loctited in. The idea of putting the wheel/axle on a pillar drill is all very well but the chassis might well get in the way. The thoughts here about a slot and then a large screwdriver sounds just the job. Actually, having sorted the loose screw it may not be necessary to remove the opposing wheel, but I'll file the suggestion away for future use.