Thank you from the advice I´ve removed sandstone form the materials :) The hole is designed this way because of two facts: 1-In plastic you dont design the threads, as the screw is always metallic, it will make the thread the first time you screw it, and this way it will fit the best possible way. 2-I´ve seen that tripod screws , althougt the same theoretical size, have very different effective diameters. As an example, I have a chinese tripod where I fitted this mount and in the first try it fitted perfectly. Later, I tried the mount in a better tripod and it was impossible to fit. I had to use a 5.5mm drill (manually) to remove a little material from the walls so it could fit. I preffer to cut in material when you need, rather than making the hole bigger, as add in wall thickness is impossible later. hope my explanation helps :)