Thread Classes 2A / 3A and 55° vs 60° Thread Angles When selecting screws, many people first look at size, material, or head type.However, in industrial equipment and precision mechanisms, the factors that truly affect fit quality and service life are often more subtle technical details: Thread Class Thread Angle These parameters determine the precision of the fit between the screw and the threaded hole, the clearance between threads, and the stability under vibration or load