Your assembly automation also affects screw choice. Some screw heads register better/faster than others depending on the size. This affects your line speed. A l

Your assembly automation also affects screw choice. Some screw heads register better/faster than others depending on the size. This affects your line speed. A line might also be building sub-assemblies that are shipped to different lines with different equipment and this a whole different set of optimized part sizes. The order you repair something isn't necessarily the order it was assembled in the factory(ies).