Hi dysondestijl, I've had an attempt at pulling the contact head wheels off, you were right they are really tight and I gave up before I broke it.
From your reply it seems that the little axle stays attached to the body of the contact head. So I was wondering if a bearing puller could be used to pull the wheels off. The way it could work is that the puller would clamp onto the inside face of the wheel and the threaded bolt would push onto the outside end of the axle. What to you think? I thought I'd check with you before I find/make a puller.