1. Standard thread

All tooth types, diameters, and pitches are in line with the national standard thread called a standard thread.

The complete marking of the thread is thread characteristic code (tooth type), dimension code (large diameter, lead, pitch, line number), tolerance zone code (top diameter and middle diameter), screwing length code (short, medium, and long), and turning code (left and right).

The code of standard thread is marked directly as dimension text, and the size code of pipe thread is qualitative so lead out the label, lead out from the large diameter.

2. Non-standard thread

The thread whose tooth type and diameter do not meet the standard is called a non-standard thread. The non-standard thread has no special code, need to mark each size, technical requirements, etc.

Standard threads should be used wherever possible.