A fastener refers to a part capable of performing a fastening function. Threaded fasteners refer to fasteners with threads, which are manufactured according to a certain size. It performs its basic function through the mutual cooperation of external and internal threads. We use this type of threaded fasteners. The function makes the threaded fastener play a great role in the connection and fastening of the object and the movement of the object. Fasteners include not only threaded fasteners, but also washers, rivets, pins, and so on.
① Fastening threads, including ordinary threads; transitional fitting threads; interference fitting threads; small threads; MJ threads.
② Transmission threads, including trapezoidal threads; serrated threads; square threads.
③ Pipe thread, 55 ° thread angle pipe thread; 60 ° thread angle pipe thread; metric taper thread; dry seal pipe thread.
④ Special threads, including threads for optical instruments; trapezoidal threads for forged steel valves; lead screws for machine tools; petroleum threads; cylinder threads, etc.
The thread is determined by the profile, diameter, pitch, number of threads, and direction of rotation (the five elements of the thread geometry). Only the five internal and external threads can be used together.
Among the five elements, tooth shape, nominal diameter, and pitch are the main three elements. National standards specify some standard tooth shapes, nominal diameters, and pitches. All those elements that meet the standard are called standard threads.
If the tooth shape meets the standard, but the nominal diameter or pitch does not meet the standard, it is called a special thread, and if the tooth shape does not meet the standard, it is called a non-standard thread.