1.Tooth type
On the section through the screw thread axis, the shape of the thread is called the profile. The angle between the flanks of two adjacent teeth is called the tooth angle. The regular thread has a triangular shape with a tooth shape angle of 60°.
2. Diameter
Major diameter: refers to the diameter of the imaginary cylinder or conical surface that coincides with the crest of the external thread of the screw and the bottom of the internal thread. The major diameter of the external thread is represented by d, and the major diameter of the interal thread is represented by D.
Minor thread diameter: refers to the diameter of the imaginary cylinder or conical surface that coincides with the tooth bottom of the external thread and the tooth crest of the internal thread. The minor diameter of the external thread is represented by d1, and the minor diameter of the external thread is represented by D1.
Pitch thread diameter: between the major diameter and the minor diameter, imagining a cylindrical surface (or cone surface), in its axial section, the tooth width and groove width on the prime line are equal, then the diameter of the imaginary cylindrical surface is called the pitch diameter.
3. Line count
The number of helixes that form the thread is called the number of threads. There are single-line and multi-line threads, and the multi-line threads are evenly distributed in the section perpendicular to the axis.
4. Pitch
The axial distance between two adjacent teeth corresponding to two points on the center diameter line is called the pitch. On the same helix, the axial distance between two adjacent teeth corresponding to two points on the center diameter line is called the lead. The relationship between the number of lines n, the pitch P, and the lead S is: S=n·P
5.Rotation
Viewed along the axis, a thread that rotates clockwise is called a right-hand thread, and a thread that rotates counterclockwise is called a left-hand thread.
The thread profile, diameters, pitch, number of lines and direction of rotation are called the five baisc elements of the thread. Only the internal and external threads with the same five elements can be screwed together.
