Hi Clive, I'll be pretty much dismantling the bearing supports and hoping to have the bearings push fit into the end sections of the aluminium plate If all goes well. I'm not too sure if that would then change your decision on what size extrusion but silly me meant 16mm screws as I'll be re-using my current ones and plenty spares. Cannot wait to get away from the terrible sbr stuff, had a nightmare of a job chasing ball bearings around the place. I'll be going for two on the X, one on each side section and one on the Y.