Types and markings of threads

1 Type of thread

Threads can be divided into connection threads and drive threads according to their uses. Refer to Table 1 for the types and uses of commonly used standard threads.

2 Drawing method of threaded connection

In the cross-sectional view as shown in Figure 2, the connecting part of the internal and external threads is drawn according to the external thread, and the remaining parts are still represented by their own drawing methods. The thick and thin solid lines of the large and small diameters of the internal and external threads should be aligned respectively.

3 Thread code marking

The thread on the drawing needs to be marked with the specified thread code. Except for pipe threads, the marking format of the thread code is:

The marking format of pipe thread is: feature code size code rotation direction

Among them, the right-hand thread is omitted without note, and the left-hand thread is represented by LH.

4 Marking of thread mark (Guide: Failure analysis and prevention of pipe thread)

When the thread precision is required to be high, in addition to marking the thread code, the thread tolerance zone code and thread engagement length should also be marked.

The marking format of the thread mark is: Thread code Thread tolerance zone code (pitch diameter, top diameter) screwing length

Explanation about marked content:

1) Tolerance zone code is represented by numbers and letters (capital letters for internal thread, lowercase letters for external thread), such as 7H, 6g, etc. It should be specially pointed out that 7H, 6g, etc. represent thread tolerance, while H7, g6 represent Cylinder tolerance code.

2) The screwing length is defined as short (indicated by S), medium (indicated by N), and long (indicated by L). Under normal circumstances, the screwing length is not marked, and the thread tolerance zone is determined by the medium screwing length (N). If necessary, you can add the code S or L of the screw length, such as M20-5g6g-L. For special needs, the value of the screwing length can be indicated, such as M20-5g6g-30.

5 The marking method of the thread mark on the view

As shown in the legend in Table 1, except for the pipe thread, the marking of the thread mark on the view is the same as the linear dimension marking method; while the pipe thread is in the form of a leader line, the leader line should be drawn from the major diameter and should not be The hatching is parallel.

Notes marked in Table 1:

1) M 16-5g6g means coarse normal thread, nominal diameter 16, right-handed, thread tolerance zone 5g middle diameter, 6g major diameter, the screw length is considered as medium length.

2) M161 LH-6G means fine-tooth ordinary thread, nominal diameter 16, pitch 1, left-handed, thread tolerance zone diameter and major diameter are both 6G, and the screwing length is considered as medium length.

3) G1 means inch non-thread sealing pipe thread, size code 1 in, right-handed.

4) Rc 12 means inch thread sealing taper pipe thread, size code 12 in, right-handed.

5) Tr208(P4) means trapezoidal thread, nominal diameter 20, double thread, lead 8, pitch 4, right-handed.

6) B202LH means serrated thread, nominal diameter 20, single thread, pitch 2, left-handed.

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