The lead angle of a screw thread is the angle formed between the helical path of the thread and a line that is perpendicular to the thread axis. This angle essentially describes how steeply the thread spirals around the screw or bolt. It is a key factor in understanding how the thread converts rotational motion into linear motion.
In contrast, the helix angle is the angle between the helix of the thread and the line parallel to the axis of the screw. It is the complement of the lead angle.
These angles influence how the thread engages with its mating part and affects the load distribution along the thread. It plays a role in the overall efficiency of the screw and the smoothness of its operation. Understanding both angles is important for designing threads that perform effectively in their intended applications.