The EF lens mount itself was thinned. It could have been thinned all the way to the edge but I decided to leave a small ridge since this would not interfere with rotation of the aperture ring when these were later combined. This ring could, in fact be fitted to the lens in lieu of the ring described in the previous slides but I decided to glue this one to the other one since this one did not have metal where the attachment screws are located. I guess this is another situation where a personal decision needs to be made and it is one of those "you have to be there" deals where it is more obvious if you see the situation in front of your eyes.