1, the use of thread and characteristics

The use of thread is very wide, from aircraft, cars to our daily life in the use of water pipes, gas and so on are used in a large number of occasions, most of the thread plays a tight connection role, the second is for the transfer of force and motion, there are some special purpose of the thread, although the variety, but their number is limited.

Because of its simple structure, reliable performance, convenient disassembly and easy manufacture, the thread has become an indispensable structural element in all kinds of mechanical and electrical products.

According to the use of threads, all kinds of threaded parts should have the following two basic functions: one is good convergence, the other is enough strength.

2. Thread classification

A. according to their structural characteristics and uses, they can be divided into four broad categories:

Ordinary thread (fastening thread) : the tooth shape is triangular, used for connecting or fastening parts. The common thread is divided into coarse thread and fine thread according to the pitch, the connection strength of fine thread is higher.

Transmission thread: tooth shape has trapezoid, rectangle, saw shape and triangle, etc. .

Sealing thread: for sealing connection, mainly pipe thread, taper thread and taper pipe thread.

Special purpose thread, referred to as the special thread.

B, according to the region (country) can be divided into: metric thread (metric thread)  thread, n thread, etc. , we are used to  thread and n thread called  thread, its tooth angle has 60 ° , 55 ° , etc. , diameter and pitch and other related thread parameters used inch size (inch) . In our country, the tooth angle is unified to 60 ° , and the diameter and pitch series in millimeter (mm) are used to name this kind of thread: ordinary thread.

3. Common thread type

4.Basic terminology for threads

Thread: on a cylindrical or conical surface, a continuous projection formed along a spiral line with a specified tooth shape.

External thread: a thread formed on the external surface of a cylinder or cone.

nternal thread: internal thread formed on the internal surface of a cylinder or cone.

Diameter: the diameter of an imaginary cylinder or cone tangent to the crown of an external thread or the base of an internal thread.

Diameter: the diameter of an imaginary cylinder or cone tangent to the base of the outer thread or the crown of the inner thread.

Meridian: the diameter of an imaginary cylinder or cone whose generatrix passes through grooves and projections of equal width. This imaginary cylinder or cone is called a medium diameter cylinder or cone.

Right-hand thread: a thread that is turned in while rotating clockwise.

Left-hand thread: a thread that is turned in when turned counterclockwise.

Tooth angle: in the thread tooth type, two adjacent tooth side angle.

Pitch: the axial distance between two adjacent teeth on the midline corresponding to the two points.

5. Thread marking

Metric thread marking:

In general, a complete metric thread marking should include the following three elements:

A represents the thread type code of thread characteristics;

B thread size: generally should be composed of diameter and pitch, for multi-thread thread, should also include the lead and line number;

C thread accuracy: the accuracy of most threads by the diameter of the tolerance zone (including the tolerance zone position and size) and the length of the combined decision.