Types of screw thread
According to the use of thread can be divided into:
1. International Metric Thread System:
Threads used in CNS of China. The top of the tooth is flat and easy to turn, while the bottom of the tooth is rounded to increase the strength of the thread. The thread Angle is 60 degrees, and the specification is expressed by M. Metric thread can be divided into coarse and fine teeth. The notation is m8x1.25. (M: code, 8: nominal diameter, 1.25: pitch).
2. American Standard Thread:
The top and root of the thread are flat, the strength is better. The thread Angle is also 60 degrees and the size is indicated by the number of teeth per inch. This thread can be divided into rough teeth (NC); Fine thread (NF); Extra fine teeth (NEF) grade 3. The notation is 1/2-10NC. (1/2: outer diameter; 10: number of teeth per inch; NC code).
3. Unified Thread:
By the United States, The United Kingdom, Canada jointly formulated, currently commonly used British thread. The thread Angle is also 60 degrees and the size is indicated by the number of teeth per inch. This thread can be divided into coarse teeth (UNC); Fine thread (UNF); Superfine teeth (UNEF). The notation is 1/2-10UNC. (1/2: outer diameter; 10: number of teeth per inch; UNC code)
4. Sharp V Thread:
Top and root are pointed, weak strength, also bad not often used. The thread Angle is 60 degrees.
