Some sewing machines come with a shorter needle clamp screw and cannot be used with certain presser feet such as a walking foot, ruffler/pleating foot, free motion darning foot, knit foot, etc. This is because the arm of those feet must go over a needle clamp screw to make it operate properly.

This screw is not the needle clamp screw but the actuating screw that goes into the needle clamp on the right side of the needle clamp.