People who engage in machinery use the most screws. There are 11 types of threads. How many do you know?

It can be divided into:
      1. International metric standard thread
      The thread adopted by my country's national standard CNS. The top of the teeth is flat and easy to turn, and the bottom of the teeth is rounded to increase the thread strength. The thread angle is 60 degrees, and the specification is indicated by M. Metric threads 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
      Both the top and the root of the thread are flat, and the strength is better. The thread angle is also 60 degrees, and the specifications are expressed in terms of how many teeth per inch. Such threads can be divided into coarse teeth (NC); fine teeth (NF); extra fine teeth (NEF) three levels. Notation is like 1/2-10NC. (1/2: outer diameter; 10: teeth per inch; NC code).
      3. Unified standard thread
      It is jointly formulated by the United States, the United Kingdom, and Canada, and is commonly used in the British thread. The thread angle is also 60 degrees, and the specifications are expressed in terms of how many teeth per inch. Such threads can be divided into coarse teeth (UNC); fine teeth (UNF); extra fine teeth (UNEF). The notation is 1/2-10UNC. (1/2: outer diameter; 10: teeth per inch; UNC code)
      4.V-shaped thread
      Both the top and the root are pointed, and the strength is weak, and it is not easy to use. The thread angle is 60 degrees.
      5. Hui type thread
      The thread adopted by the British National Standard. The thread angle is 55 degrees, indicating that the symbol is "W". Suitable for rolling method manufacturing. The notation is as W1/2-10. (1/2: outer diameter; 10: teeth per inch; W code).
      6. Round thread
      It is the standard thread set by German DIN. Suitable for connection of light bulb and rubber tube. The symbol is "Rd".
      7. Pipe thread
     In order to prevent leakage, the thread is often used to connect gas or liquid pipe fittings. The thread angle is 55 degrees, which can be divided into straight pipe thread codes "P.S., N.P.S." and inclined pipe thread codes "N.P.T.", and its taper is 1:16, that is, 3/4 inch per foot.
      8. Square thread
      The transmission efficiency is large, second only to the ball thread, and it cannot be adjusted with a nut after wear, which is its disadvantage. Generally used for the screw of the vise and the thread of the crane.
      9. Trapezoidal thread
      Also known as Arkham thread. The transmission efficiency is slightly smaller than the square thread, but the nut can be used to adjust after wear. The metric thread angle is 30 degrees, and the inch thread angle is 29 degrees. Generally used for lead screw of lathe. The symbol is "Tr".
      10. Zigzag thread
      Also known as rhombic thread, it is only suitable for unidirectional transmission. Such as screw jacks, presses, etc. The symbol is "Bu".
      11. Ball thread
      It is the thread with the best transmission efficiency, which is difficult to manufacture and extremely expensive. It is used in precision machinery. Such as the lead screw of CNC machine tool.
      Representation of inch bolts
      LH 2N 5/8 × 3-13 UNC─ 2A
      (1) LH is the left thread (RH is the right thread, which can be omitted).
      (2) 2N double thread.
      (3) 5/8 inch thread, outer diameter 5/8".
      (4)3 Bolt length 3”.
      (5)13 threads with 13 teeth per inch.
      (6) UNC unified standard thread coarse teeth.
      (7) Level 2 fit, external thread (3: tight fit; 2: medium fit; 1: loose fit) A: external thread (can be omitted) B: internal thread
      Inch thread: The size of an inch thread is usually expressed by the number of threads per inch on the thread, referred to as "the number of teeth per inch", which is exactly equal to the reciprocal of the pitch. For example, a thread with 8 teeth per inch has a pitch of 1/8 inch.

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