Dan

That would be excellent thanks. I will be in touch.

Gary C

All is clear now thankyou. My new NV toy does not have any square bits on the clamp screws but it does have two sets of holes across the mount sideplates which appear to be about 3mm below the top of the rail. I assume these will line up with the slots in the rail so a stop block could be fitted. I have no doubt it will be evident when I borrow Dan's rail to measure