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Main Geometric Parameters Of Cylindrical Thread

Oct 16, 2019

1 outer diameter (large diameter), the diameter of the imaginary cylinder that coincides with the external thread crest or the internal thread root. The nominal diameter of the thread is the large diameter.


2 inner diameter (small diameter), the diameter of the imaginary cylinder that coincides with the external thread or the internal thread crest.


3 medium diameter, the busbar passes through the diameter of the imaginary cylinder with the same width of both the protrusion and the groove on the tooth profile.


4 pitch, the axial distance between adjacent points on the medium diameter line corresponding to two points.


5 lead, the axial distance between two points on the same diameter on the same spiral line.


6 tooth angle, the angle between the adjacent two flank on the thread profile.


7 Threaded angle, the angle between the tangent of the helix on the middle diameter cylinder and the plane perpendicular to the axis of the thread.


8 working height, the distance between the two-phase matching thread on the mutually overlapping portions in the direction perpendicular to the axis of the thread. The nominal diameter of the thread is the nominal diameter of the outer diameter of the pipe except that the inner diameter of the pipe is the nominal diameter. The thread has been standardized, with metric (metric) and imperial systems, and the international standard is metric.


Except for the pipe thread with the pipe diameter as the nominal diameter, the other threads have the nominal diameter of the outer diameter. The thread pair whose thread angle is smaller than the friction angle does not loosen under the action of the axial force, and is called self-locking, and its transmission efficiency is low.


Among the cylindrical threads, the triangular thread has good self-locking performance. It is divided into two types: coarse teeth and fine teeth. Fine teeth have small pitch, small angle of lift and better self-locking performance. They are often used in thin-walled tubes of small parts, with vibration or variable load connections, and fine-tuning devices.


The shape of the taper thread is triangular, mainly relying on the deformation of the tooth to ensure the tightness of the thread pair, and is mostly used for the pipe fitting.



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