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Do You Know What A Thread Is

Jan 04, 2020

All components and parts with standardized structure and size are called standard parts, such as bolts, screws, studs, nuts, washers, keys, pins, rolling bearings, etc. Parts whose structure and size are partially standardized are called common parts, such as gears and springs.


 Basic knowledge of threads


 Formation of threads


Spiral bodies formed by plane graphics such as triangles, rectangles, etc. that are coplanar with the axis of the revolution plane are called threads. Threads are parts


A common structure above, there are two types of external and internal threads, generally used in pairs.


Basic elements of threads


(1) Tooth profile The thread is cut with a plane passing through the thread axis, and the resulting cross-sectional shape is called the thread profile. Common thread teeth are triangular, trapezoidal, zigzag and rectangular. Different thread types have different uses, see Table 6-1.


(2) Diameter


There are three diameters of the thread: large diameter (d or D), small diameter (d1 or D1), and medium diameter (d2 or D2), as shown in Figure 6-3. The large diameter of ordinary threads and trapezoidal threads is also called the nominal diameter. The top diameter of the thread is the diameter of the top circle of the tooth, that is, the large diameter of the external thread, and the small diameter of the internal thread;


(3) Number of lines n


There are single and multiple threads. Threads formed along one helix are called single-thread threads, as shown in Figure 6-4 (a); threads formed along more than two helix are called multi-thread threads, as shown in Figure 6-4 (b).


(4) pitch P and lead Ph


The axial distance between the corresponding points of two adjacent threads on the medium diameter line is called the pitch. A turn along the same spiral line, the distance moved axially is called the lead. The lead of a single-thread thread is equal to the pitch, that is, Ph = P; the lead of a multi-thread thread is equal to the number of lines multiplied by the pitch, that is, Ph = nP. As shown in Figure 6-4.


(5) Rotation


There are two types of threads: right-handed and left-handed. Threads processed according to the right helix and clockwise are called right-handed threads, otherwise they are called left-handed threads. See Figure 6-5. Right-handed threads are commonly used in engineering.