There are eleven types of threads, how many do you know?
1. International metric standard thread
The thread used by my country’s national standard CNS. The top of the tooth is flat and easy to turn, and the bottom of the tooth is arc-shaped to increase the strength of the thread. The thread angle is 60 degrees, and the specification is represented by M. Metric threads can be divided into two types: coarse thread and fine thread. Notation such as 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, with better strength. The thread angle is also 60 degrees, and the specification is expressed in teeth per inch. This kind of thread can be divided into three grades: coarse thread (NC); fine thread (NF); extra fine thread (NEF). Notation such as 1/2-10NC. (1/2: outer diameter; 10: teeth per inch; NC code).
3. Unified standard thread
Jointly formulated by the United States, the United Kingdom, and Canada, it is the commonly used inch thread at present. The thread angle is also 60 degrees, and the specification is expressed in teeth per inch. This kind of thread can be divided into coarse thread (UNC); fine thread (UNF); extra fine thread (UNEF). Notation such as 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, the strength is weak, and it is not often used because it is easy to break. Thread angle is 60 degrees.
5. Whirlpool thread
Threads adopted by British National Standards. The thread angle is 55 degrees, which means the symbol is “W”. Suitable for rolling method manufacturing. Notation such as W1/2-10. (1/2: outer diameter; 10: teeth per inch; W code).
6. Round thread
Standard thread according to German DIN. It is suitable for the connection of light bulbs and rubber tubes. The symbol is “Rd”.
7. Pipe thread
Threads used to prevent leakage are 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 the taper is 1:16, that is, 3/4 inch per foot.
8. Square thread
The transmission efficiency is high, second only to the ball thread, and it cannot be adjusted with the nut after wear and tear, which is its disadvantage. Generally used for the screw of the vise and the thread of the crane.
9. Trapezoidal thread
Also known as Acme thread. The transmission efficiency is slightly smaller than that of the square thread, but it can be adjusted with a nut after wear. The metric thread angle is 30 degrees, and the imperial thread angle is 29 degrees. Typically used for lead screws in lathes. The symbol is “Tr”.
10. Zigzag thread
Also known as oblique thread, it is only suitable for one-way transmission. Such as screw jacks, pressurizers, etc. The symbol is “Bu”.
11. Ball thread
The thread with the best transmission efficiency is difficult to manufacture and the cost is extremely high, and it is used in precision machinery. Such as the lead screw of CNC machine tools.
Representation of imperial bolts:
LH 2N 5/8 × 3 – 13 UNC━ 2A
(1) LH is left thread (RH is right thread, can be omitted)).
(2) 2N double thread.
(3) 5/8 inch thread, 5/8” OD.
(4) 3 bolt length 3”.
(5) 13 threads have 13 teeth per inch.
(6) UNC unified standard thread coarse pitch.
(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 the inch thread is usually expressed by the number of threads per inch of length 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.