The diameter of the thread is divided into large diameter (D or d), small diameter (D1 or d1) and middle diameter. The large diameter of ordinary thread and ladder thread is also called the nominal diameter. The top diameter of the thread is the diameter of an imaginary cylinder or cone that is tangent to the top of the external or internal thread, that is, the large diameter of the external thread or the small diameter of the internal thread; the bottom diameter of the thread is tangent to the bottom of the external or internal thread The diameter of an imaginary cylinder or cone, that is, the small diameter of an external thread or the large diameter of an internal thread.
There are left-handed and right-handed threads. Threaded clockwise is called right-handed thread, and counter-clockwise is called left-handed thread. Right-handed thread is commonly used in engineering.
Number of threads
Threads are divided into single and multiple threads. Threads formed along one spiral are called single threads, and threads formed along more than two spirals are called multi-threads. The connecting threads are mostly single wires.
Pitch and lead
The axial distance between two adjacent points of the thread on the middle diameter line is called the pitch. Rotate a circle along the same spiral, and the axial movement distance is called the lead. The lead of a single-thread thread is equal to the pitch, and the lead of a multi-thread thread is equal to the number of pitch X lines.
Example: M 10 × 1 LH –7H-L
M represents the common thread characteristic code;
10 × 1 means nominal diameter × pitch, coarse teeth do not pay pitch;
LH indicates the left-hand thread code, and the right-hand thread does not indicate the rotation direction code;
7H is the tolerance zone code;
L represents the code of the twist length group. Group codes are not noted for medium lengths, and specific length values are noted when special needs are required.