A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is an inclined plane wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. More screw threads are produced each year than any other machine element.
Threads are generally produced according to one of the many standards of thread systems. Standards Development Organizations such as the American National Standards Institute, American Society of Mechanical Engineers, SAE International, International Organization for Standardization, Deutsches Institut für Normung (German Institute for Standardization), British Association and others produce these standards for manufacturers to follow when producing threaded components.
Today let’s talk about the basic knowledge of thread:
1.Male and Female
Every matched pair of threads, external and internal, can be described as male and female. For example, a screw has male thread, while the matching hole has female thread.
The helix of a thread can twist in two possible directions. Most threads are oriented so that the threaded item when seen from a point of view on the axis through the center of the helix, moves away from the viewer when it is turned in a
clockwise direction, and moves towards the viewer when it is turned counter clockwise. By common convention, right-handedness is the default handedness for screw threads. Therefore, most threaded parts and fasteners have righthanded threads.
The type of thread can be identified by the following characteristics.
The pitch is the distance from the crest of one thread to the next in mm. TPI (Threads per inch) is used by inch thread.
The major diameter is determined by the thread tips.
The minor diameter is determined by the groove of the thread.
The pitch diameter is the distance of two opposite flanks or the distance of the centreline of
The flank angle is the angle between the flank of a screw thread and the perpendicular to the axis of the
screw. Tapered threads have a taper angle. This is the angle between the taper and the centre axis of the
The outer-most part of the thread is called crest, the inner-most part of the
thread is called root.