I was at a Bisley shoot recently where one of my companions had a later version A.I AX. He mentioned that the thumb screws securing the cheek height and Length of pull kept working loose. I advised him to use the hex wrench stowed in the cheek piece to nip it up once set to his desired position. That is when we discovered that the newer version AX has solid thumb crews with no access to the allen screws and is therefore not able to be tightened with the hex wrench. This seems to me to be a retrograde step in the design.