Fastener Thread Types And Geometric Parameters

Fastener threads are a type of cross-section on a solid outer or inner surface that has a uniform spiral protrusion shape. According to the structural characteristics and uses of fastener threads, they are mainly divided into three types. Therefore, Xiaorui will provide a detailed introduction for everyone.

Fastener thread type:

1, Regular thread: The tooth shape is a triangle, used for connecting or fastening parts. Ordinary threads are divided into two types based on pitch: coarse thread and fine thread, with fine thread having higher connection strength.

2, Transmission thread: The tooth shape includes trapezoidal, rectangular, saw shaped, and triangular shapes.

3, Sealing thread: used for sealing connections, mainly for pipe threads, taper threads, and taper pipe threads.

To gain a better understanding of the use of fasteners, it is essential to consider the main geometric parameters of mechanical fastener threads. The main geometric parameters of mechanical fastener threads include:

1, Major diameter/tooth outer diameter (D, d): Refers to the hypothetical cylindrical diameter where the top or bottom of the external thread coincides. The major diameter of a thread basically represents the nominal diameter of the thread size.

2, Mid diameter (D2, d2): D2=d2=D (d) -2x3H/8, where H is the height of the original triangle:

3, Minor diameter/tooth base diameter (D1, d1): The diameter of an imaginary cylinder where the top of an external or internal thread coincides. H=(√ 3/2) P=0.866025P (60O Yashanjiao); H=0.960491P (55 O Yashanjiao)

4, Pitch (P): refers to the axial distance between two points corresponding to adjacent teeth on the centerline or the distance between adjacent teeth or two adjacent tooth valleys. In the British system, tooth pitch is indicated by the number of teeth per inch (25.4 mm) (as shown in the table below).

5, Half angle of tooth shape( α/ 2) The angle between the perpendicular line of the tooth side and the thread axis is 60O/2 for regular thread profiles and 55O/2 for BSW thread profiles. The general angle of the wooden screw tooth is 60 degrees, and the angle of the tail tip is 60 degrees.

6, Thread rotation length: refers to the length of the mutually rotating parts along the thread axis of a two-phase mating thread.