Thank you everyone for the info... the one thing I have is plenty of wood screws from the days of when Screwfix sold mainly screws and they sold good mixed size trade packs.. Its another job to set right, but I am glad I found that the light was hanging off before it was lost completely. I might create two half round spacers from stainless round bar that would fit and fill most of the slots rather that relying on the screw head to clamp ( once I know where the lights height should be for my spare ) this would provide a more secure clamping force over the slot area with less slop. Again, many thanks to everyone for feedback.
Dave
