I have a Hymer MH with concertina window blinds to the side and front. These are guided by a steel rail which appears to be fixed to the side of the van with a metal disc through which comes a screw which is attached to the rail. Some hamfisted twit i.e. me has leaned on the rail and sprung it off the screw thread. Easy. New Screw and off we go ! Ah. but how is the metal disc through which the screw comes fixed to the van? Does it pop off or screw off or what? Did they build the van around it ? Can anyone help.