Dear Keith
I don't have a photo, and we shan't be on Delphine to take one until next weekend at the earliest - but I thought I'd try a description. Our device is a rectangular plate with one of the shorter edges rounded to form a short section at right angles to the main plate. There's a slot in the main plate and a threaded hole in the mast. From memory, I guess the hole is M6 - but this could be wrong!
The plate sits on the mast with the short edge in the groove in the mast, and the slot in the main plate lined up over the threaded hole in the mast. You need a bolt through the slot in the plate into the threaded hole (ours has an Allen key head but a pan or rounded screw head would do just as well). The slot allows the plate to slide a little bit from one side to the other, and the bolt should be tightened so that the plate is as far across the groove in the mast as possible, this reducing its width so that sail slugs can't fall out. We had an early problem on Delphine that one of the sail slugs came out easily, and we solved this by releasing the bolt, sliding the plate as far as it would go across the groove in the mast, and then re-tightening it.
Your experience has made me think that it would be a good idea to identify a spare bolt, as it would be very easy to drop and lose the one in the mast!
Best wishes
Gilliane
Delphine, Parker 275, no. 41