What are the main types of threads

Update:20-10-2020
Summary:

A screw can be seen everywhere, but there are many type […]

A screw can be seen everywhere, but there are many types of screws and complex specifications. Especially nowadays, people’s requirements for product quality and performance are getting higher and higher. Many manufacturers design their own screws and require screw manufacturers to follow their own drawings. Processing and production increase the difficulty of screw manufacturing.

Today we will take a look at the thread types of screws, which can be divided into different thread uses:

1. International metric standard thread

The thread used in my country's national standard CNS. The tooth top is flat, which is easy to turn, and the tooth bottom is arc-shaped to increase the thread strength. 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. The notation is M8x1.25. (M: code, 8: nominal diameter, 1.25: pitch)

2. American standard thread

Both the top and root of the thread are flat and the strength is better. The thread angle is also 60 degrees, and the specification is expressed by a few teeth per inch. This kind of thread can be divided into coarse thread (NC); fine thread (NF); extra fine thread (NEF) level three. The notation is like 1/2-10NC. (1/2: outer diameter; 10: number of teeth per inch; NC code)

3. Unified standard thread

It is jointly formulated by the United States, the United Kingdom, and Canada, and is the currently commonly used inch thread. The thread angle is also 60 degrees, and the specification is expressed by a few teeth per inch. This kind of thread can be divided into coarse thread (UNC); fine thread (UNF); extra fine thread (UNEF). The notation is like 1/2-10UNC. (1/2: outer diameter; 10: number of teeth per inch; UNC code)

4. V-shaped thread

The top and root are both pointed, weak in strength, and not often used easily. The thread angle is 60 degrees.

5. Thread used in British National Standard

The thread used in the British National Standard. The thread angle is 55 degrees, and the symbol is "W". Suitable for manufacturing by rolling method. The notation is like W1/2-10. (1/2: outer diameter; 10: number of teeth per inch; W code)

 

 

6. Round thread

One is the standard thread defined by German DIN. Suitable for the connection of bulbs and rubber tubes. Indicates that the symbol is "Rd"

7. Thread for pipe

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 code "P.S., N.P.S." and oblique pipe thread code "N.P.T.", 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 a nut after wear, which is a disadvantage. Generally used for the screw of the vise and the screw of the crane

9. Trapezoidal thread

One is also called Akem thread. The transmission efficiency is slightly lower 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 inch thread angle is 29 degrees. Generally used in the lead screw of a lathe. Indicates that the symbol is "Tr"

10. Serrated thread

One is also called oblique thread, which is only suitable for unidirectional transmission. Such as screw jacks, presses, etc. Indicates that the symbol is "Bu"

11. Ball thread

The thread with the best transmission efficiency is difficult to manufacture, and the cost is extremely high. It is used in precision machinery. Such as the lead screw of a CNC machine tool

The representation of inch bolts: LH 2N 5/8 × 3-13 UNC-2A (1) LH is left-hand thread (RH is right-hand thread, can be omitted)). (2) 2N double thread thread. (3) 5/8 inch thread, outer diameter 5/8 ". (4) 3 bolt length 3". (5) 13 thread counts 13 teeth per inch. (6) UNC uniform standard thread coarse thread. (7) Level 2 fit, external thread (3: tight fit; 2: middle fit; 1: loose fit) A: external thread (can be omitted) B: internal thread. Inch thread: the size of the inch thread, usually expressed by the number of threads per inch of length, referred to as "number of threads per inch", which is exactly 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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