Screw thread, dealing with machinery every day, domestic and foreign for a long time, metric and imperial, straight cone, sealed and non-sealed, inner and outer, 55 degrees and 60 degrees. In short, it is often messed up. Use it once to check from beginning to end. I can also summarize it here. I hope it can be helpful.
My method is to print it out and put it on the side of the table, and check it at any time when I use it. After a long time, I will remember it naturally.
NPT is a general purpose American standard tapered pipe thread with a profile angle of 60°
The PT tooth is an imperial tapered thread, and the tooth angle is 55°, which is the most commonly used in sealing. The British pipe thread is a fine thread, because the tooth depth of the coarse thread will seriously reduce the strength of the pipe with the outer diameter of the cut thread.
PF teeth are parallel threads for pipes.
G is a 55-degree non-threaded sealing pipe thread, which belongs to the Whitworth thread family. Marked as G stands for cylindrical thread, G is the general name of pipe thread (Guan), and the division of 55 and 60 degrees is functional
ZG is commonly known as pipe cone, that is, the thread is processed by a conical surface. The general water pipe joints are like this. The old national standard is marked as Rc
The metric thread is represented by the pitch, and the American and British thread is represented by the number of threads per inch. This is the biggest difference between them. The metric thread is a 60-degree equilateral tooth type, and the British system is an isosceles 55-degree tooth type. The American thread 60 degrees. Use metric units for metric threads and imperial units for US and British threads.
Pipe thread is mainly used for the connection of pipes, and its internal and external threads are closely matched, and there are two types of straight pipe and tapered pipe. The nominal diameter refers to the diameter of the connected pipe, obviously the major diameter of the thread is larger than the nominal diameter.
1/4, 1/2, 1/8 are the nominal diameters of British thread, in inches.
1. Inch unified thread
Widely used in inch system countries, this type of thread is divided into three series: coarse thread series UNC, fine thread series UNF, extra fine thread series UNFF, plus a fixed pitch series UN.
Marking method: thread diameter - number of teeth per inch series code - precision grade
Example: Coarse series 3/8—16UNC—2A
Fine teeth series 3/8—24UNF—2A
Extra fine tooth series 3/8—32UNFF—2A
Fixed pitch series 3/8—20UN—2A
The first digit 3/8 indicates the outer diameter of the thread, the unit is inches, and the conversion to the metric unit mm is multiplied by 25.4, that is, 3/8×25.4=9.525mm; the second and third digits 16, 24, 32, and 20 are The number of teeth per inch (the number of teeth on the length of 25.4mm); add WeChat: Yuki7557 to send a copy of the macro program tutorial, the text code after the third digit is UNC, UNF, UNFF, UN is the series code, and the last two digits are 2A for accuracy grade.
2. Transformation of 55°cylindrical pipe thread
55°cylindrical pipe thread is derived from the inch system, but it is widely used in both metric and inch countries. It is used to connect pipe joints and pipes for conveying liquids, gases, and installing wires. However, the codes of various countries are different, and they should be pressed The foreign codes in the table (comparison table) are converted into Chinese codes, and the 55° cylindrical pipe thread codes of various countries are listed in the table below. Click on the picture to get 10G CNC programming tutorial for free
country code
China
Japan G, PF
British BSP, BSPP
France
Germany R (internal thread), K (external thread)
Former Soviet Union G, TPУБ
ISO Rp
3. Transformation of 55° conical pipe thread
55° conical pipe thread means that the thread angle is 55° and the thread has a taper of 1:16. This series of threads is widely used in the world, and its code name is different from country to country, as shown in the table below. Convert the foreign codes in the table below into Chinese codes.
country code
China ZG, R (external thread)
British BSPT, R (external thread), Rc (internal thread)
France G (external thread), R (external thread)
German R (external thread)
Japan PT, R
ISO R (external thread), Rc (internal thread)
4. Transformation of 60° conical pipe thread
The 60° conical pipe thread refers to the pipe thread with a thread angle of 60° and a thread taper of 1:16. This series of threads is used in my country's machine tool industry, the United States, and the former Soviet Union. Its code name was defined as K in the past in my country, and later as Z, and now it is changed to NPT. See the table below for the thread code comparison table.
country code
China Z(Old) NPT(New)
United States NPT
soviet union
5. Transformation of 55° trapezoidal thread
Trapezoidal thread refers to the metric trapezoidal thread with a profile angle of 30°. This series of threads is relatively unified at home and abroad, and its code names are also quite consistent. See the thread codes below
country code
China T(old)Tr(new)
ISO Tr
Germany Tr
Former Soviet Union Tr
Thread Classification
According to the different uses of threads, it can be divided into:
1. International Metric Thread System
The thread adopted 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 (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), and extra fine thread (NEF). Notation such as 1/2-10NC. (1/2: outer diameter; 10: teeth per inch; NC code).
3. Unified Thread (UnifiedThread)
Jointly formulated by the United States, the United Kingdom, and Canada, it is the most 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 (Sharp VThread)
Both the top and the root are pointed, the strength is weak, and it is not often used. The thread angle is 60 degrees.
5. Whitworth Thread
Threads adopted by British National Standards. The thread angle is 55 degrees, and 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 (KnuckleThread)
It is a standard thread set by DIN in Germany. It is suitable for the connection of light bulbs and rubber tubes. The symbol is "Rd".
7. Pipe thread (PipeThread)
For the thread used to prevent leakage, add WeChat: Yuki7557 to send a copy of the macro program tutorial, which 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 the taper is 1:16, that is, 3/4 inch per foot.
8, square thread (SquareThread)
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 thread angle of the metric system is 30 degrees, and the thread angle of the imperial system is 29 degrees. Generally used for the lead screw of lathe. The symbol is "Tr".
10. Buttress 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, so it is used in precision machinery. Such as the lead screw of CNC machine tools.
Representation of inch bolts:
LH 2N 5/8 × 3 - 13UNC-2A
(1) LH is left thread (RH is right thread, which 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 threads per inch.
(6) UNC unified standard thread coarse thread.
(7) Level 2 fit, external thread (3: Tight fit; 2: Medium fit; 1: Loose fit) A: External thread (can be omitted) B: Internal thread
Imperial 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 "threads 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.
