I have had success converting screw-in filters to Noblex 120 magnetic filters and wanted to pass it on. In my case I had some 52mm red and orange filters lying around. I simply used the thin self-adhesive refrigerator magnet material (which can be easily cut with scissors). I chose the flat side of the filter (the side that would be next to the camera lens if screwed in) on which to apply the magnet. I applied the magnets in two strips, leaving about 1 inch of glass in between. The real Noblex filters have a 13/16" open area and a magnet that runs all the way around.

They are as easy to insert and remove as the original Noblex filters and this process opens the possibility of using any screw-in type filter in any size that will cover the lens.