just bought one for our new viv, cant tighten it enough to grip onto the glass, it keeps sliding about, the more i tighten it the screws start tightening at an angle and the metal bends making it hard to get the lock/key part on. any ideas.

maybe put a peice of rub/soft plastic between the scew and the plastic, as the rubber will provide better grip on the glass compared to the metal

We had the same prob with the locks on our vivs. In the end we gave up on them and now use the rubber wedges which we find much easier when it comes to feeding and cleaning out our snakes. It might be worth you trying them for yourself.
Hope this helps