Thanks for the replies.
So Trident made the Rattraps. This says RATRAP, (only 1 T). Typo I guess?
The "nuts" must be critical because there must be a reason for them being there, but all they do is swivel on the threaded rods.
I've tried turning the Turnbuckle type thing with a screwdriver, and still can't see exactly what it does, but I'll keep trying.
At first I thought I had to unscrew the heel section screws and use alternative holes,(as shown in the centre photo), but they may just be there to move the foot closer to the toe or heel edge.
Tridd