Differences Among Several Commonly Used Threads Such As NPT, PT, G, ZG, RC, And M

Threads, as an important mechanical connection element, are widely used in various fields. Different types of threads have significant differences in structure, performance, and application. This article will introduce in detail the differences among several commonly used threads like NPT, PT, G, ZG, RC, and M to help readers better understand and choose to use these threads.

I. NPT Thread

NPT thread, namely National Pipe Thread, is a 60-degree tapered pipe thread and is widely used in North America. The characteristic of NPT thread is that its taper is 1:16, that is, the taper changes by 1/16 inch per inch. This design enables the NPT threaded joint to fit tightly with the inner wall of the pipe, thus achieving a reliable sealing effect. The specifications of NPT thread are in inches. Common markings include 1/4, 1/2, 1/8, etc., and these markings refer to the diameter of the thread size.

The NPT threaded joint has the following advantages:

Good sealing performance: With the design of tapered pipe thread, it can fit tightly with the inner wall of the pipe to achieve a reliable sealing effect.

High pressure and temperature resistance: Made of high-quality materials, it can withstand relatively high pressure and temperature.

Reliable connection: It is connected to the pipe by rotating the thread, and the connection is firm and not easy to loosen or leak.

Simple installation: The connection can be completed by simply inserting the pipe into the joint and rotating it by a certain angle.

Wide range of application: It is applicable to various pipeline systems, such as the fields of petroleum, chemical engineering, pharmaceuticals, food processing, etc., and can also be used in pneumatic and hydraulic systems.

When using NPT thread, the following points should be noted:

Ensure that the inner wall of the pipe is clean without foreign objects and grease to guarantee the sealing effect.

The length of the pipe inserted into the joint should be appropriate. It should not be too long or too short, so as not to affect the sealing effect and service life.

Use appropriate wrenches or tools to rotate the thread. Do not use excessive or insufficient force to avoid damaging the thread or resulting in an unsteady connection.

Regularly check the sealing effect and usage of the NPT threaded joint, and replace damaged joints or repair leakage parts in a timely manner.

II. PT Thread

PT thread, namely British Standard Taper Pipe Thread, is a 55-degree tapered pipe thread with a taper of 1:16. The characteristic of PT thread is that its pitch is relatively small, and the heights of the thread crest and thread root are also small, making the thread structure more compact and effectively improving the sealing performance of the connection. The thread angle of PT thread is 60 degrees, which can withstand relatively large axial pressure and has strong compressive capacity.

The PT thread standard is mainly applicable to some pipeline connections with relatively high requirements for sealing performance, such as hydraulic systems, pneumatic systems, liquefied gas transmission pipelines, etc. PT thread has the following advantages:

Good sealing performance: The compact thread structure can effectively improve the sealing performance of the connection.

Convenient installation: With a small pitch, the connection can be completed with only a small rotation angle during installation.

Strong compressive capacity: It can withstand relatively large axial pressure and has strong compressive capacity.

PT thread has a wide range of applications. Especially in the fields of hydraulic systems, pneumatic systems, and liquefied gas transmission pipelines, due to its excellent sealing performance and installation convenience, PT thread has been widely used.

III. G Thread

G thread, namely 55-degree non-sealing pipe thread, belongs to the Whitworth thread family. The characteristic of G thread is that it has a high degree of international standardization, with unified parameters and symbol representations, which helps to reduce problems in communication and cooperation and improve work efficiency. The size of G thread is usually marked in inches, such as 1/4, 1/2, 1/8, etc., and these markings refer to the diameter of the thread size. In practical applications, the industry usually uses "fen" to describe these sizes. For example, 1/4 inch is 2 fen.

G thread has the following advantages:

High degree of standardization: With unified parameters and symbol representations, it helps to improve work efficiency.

Quick installation: The design makes the installation and disassembly process simple and fast, without requiring too many tools and time.

Strong connection stability: It has good thread engagement performance, can withstand relatively large tensile and shear forces, and effectively prevents thread loosening.

Wide range of application: It is widely used in many industries such as mechanical equipment, auto parts, construction, and engineering.

G thread plays an important role in factory production lines, automobile assembly and maintenance work, and the construction process of buildings and structures. Due to its characteristics of quick installation and disassembly, G thread greatly improves the maintenance and replacement efficiency of mechanical equipment, ensures the performance and safety of automobiles, and fixes and connects various components.

IV. ZG Thread

ZG thread, namely tapered pipe thread, is a connection standard for sealing pipe threads. The characteristic of ZG thread is its tapered thread shape, which can form a tighter seal during the connection process, thus ensuring that the fluid does not leak. In China's old mechanical drawing standards, ZG thread was expressed as ZG, and now it has been changed to R/R1/R2 (external thread) and RC (internal thread).

ZG thread has the following advantages:

Good sealing performance: The tapered design makes the contact area between the threads gradually increase during the tightening process, thus achieving a better sealing effect.

High connection strength: Due to the tapered structure of the thread, the fastening force during connection is greater, improving the strength and stability of the connection.

Wide range of application: It is widely used in many fields such as petrochemical, water conservancy and hydropower, pharmaceuticals, and food processing.

ZG thread plays an irreplaceable role in occasions where it is necessary to prevent fluid leakage due to its excellent sealing performance and stability.

V. RC Thread

RC thread, namely cylindrical external thread, is a type of thread widely used in mechanical connections. The thread profile of RC thread is smoother than that of triangular thread, so the force it bears is more uniform, and it also has better self-locking performance. The size and specification standards of RC thread are mainly designed and produced with reference to the standard of GB/T 193-1981 "Cylindrical External Thread".

RC thread has the following characteristics:

High precision: It has relatively high dimensional accuracy and geometric tolerance, which can ensure the quality of the measured thread.

Simple structure: It is mainly composed of a threaded shaft and a threaded sleeve, and is convenient to use.

Strong universality: It covers a wide range of thread specifications and can meet the needs of various different occasions.

RC thread is widely used in the fields of mechanical manufacturing, precision instruments and meters, aerospace, etc. In the mechanical manufacturing industry, RC thread is used to test the thread quality of mechanical parts to ensure the interchangeability and reliability of the parts; in the precision instruments and meters, RC thread is used to test the threads of precision instruments and meters to ensure their accuracy and stability; in the aerospace field, RC thread is used to test high-precision threads to ensure the safety and performance of aircraft and equipment.

VI. M Thread

M thread, namely metric thread, also known as international metric thread, is a commonly used thread in China. The characteristic of M thread is that its thread profile is 60 degrees, and the pitch refers to the distance between two thread crests. The standard pitch values are arranged according to the law of segmented arithmetic sequence. The specification parameters of M thread are determined in metric units (millimeters), and are expressed as M + nominal size of the major diameter of the thread × pitch.

M thread has the following advantages:

Unified measurement unit: With millimeter as the unit, it is convenient for measurement and calculation.

Standard pitch: The pitch values are arranged according to the law of segmented arithmetic sequence, which is convenient for selection and use.

Wide range of application: It is widely used in the fields of machinery, electronics, instruments and meters, automobiles, aerospace, etc.

The selection and use of M thread need to determine the diameter and pitch of the thread according to specific usage scenarios and requirements. Generally speaking, the larger the thread diameter, the stronger the load-bearing capacity, but it will also increase the weight and cost; the pitch will affect the fastening force and rotation speed of the thread. Common applications of M thread include the assembly of electronic products and precision instruments, the fastening of large mechanical equipment, etc.