1. The basic tooth Home Tools Suppliers of ordinary fastener threads The geometric parameters of fastener threads depend on the basic tooth profile in the axial section of the fastener thread. The basic profile is the theoretical profile shared by the internal and external threads formed by cutting off the top of the original triangle (equoslateral triangle) by H/8 and the bottom by cutting H/4. The tooth form is the basic size with thread. Figure 1 Basic profile of common thread of fasteners (1)

Major diameter D or d Major diameter refers to the diameter of an imaginary cylinder that coincides with the bottom of the internal thread or the top of the external thread. The major diameter of the internal thread is represented by D; the major diameter of the external thread is represented by d. (2) Minor diameter D1 or d1 Minor diameter refers to the diameter of an imaginary cylinder that coincides with the crest of the internal thread or the bottom of the external thread.

The minor diameter of the internal thread is represented by D1; the minor diameter of the external thread is represented by d1. (3) Pitch diameter D2 or d2 pitch diameter refers to the diameter of an imaginary cylinder or cone. The generatrix of the cylinder or cone passes through the place where the grooves and protrusions on the thread form are equal in width. This imaginary cylinder is called a pitch cylinder. The generatrix of the pitch cylinder is called the pitch line, and its axis is the thread axis.

The basic size of the combined inner and outer thread pitch diameters is equal, that is, D2=d2. (4) A single pitch diameter is an imaginary cylinder diameter. The generatrix of the cylinder passes through the place where the alveolar width is equal to half of the basic pitch, regardless of the width of the tooth body, to represent the actual size of the pitch diameter of the thread. (5) Pitch P The pitch refers to the axial distance between two adjacent points on the pitch generatrix. (6)

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