Thread Content
=========================================================== NPT is the abbreviation for National (American) Pipe Thread; it represents a 60-degree tapered pipe thread standard used in North America. **The relevant standard can be found in GB/T12716-1991.** NPT is also known as National (American) Pipe Thread, and it is a 60-degree tapered pipe thread standard applicable in North America. **The standard can be referred to in GB/T12716-1991.** PT is the abbreviation for Pipe Thread; it refers to a 55-degree sealed tapered pipe thread that belongs to the Whitworth thread family, and it is commonly used in Europe and the Commonwealth countries. It is frequently utilized in the water and gas piping industries, with a taper ratio of 1:16. **The standard can be found in GB/T7306-2000.** G refers to a 55-degree non-threaded sealed pipe thread that also belongs to the Whitworth thread family; the designation “G” indicates a cylindrical thread. **The standard can be referred to in GB/T7307-2001.** Additionally, the designations 1/4, 1/2, and 1/8 in relation to threads refer to the diameter of these threads, measured in inches. Those in the industry usually refer to thread sizes in terms of “minutes”; one inch equals 8 minutes, so 1/4 inch is equivalent to 2 minutes, and so on. It seems that “G” is simply a general term for pipe threads; the distinctions between 55-degree and 60-degree threads are based on functional considerations, and they are commonly referred to as round pipe threads. That is, the thread is formed by machining a cylindrical surface. ZG is commonly known as pipe thread, meaning that the threads are formed by a conical surface; most standard pipe fittings use this type of thread. The old national standard designates it as Rc. ------------------------------------------------------ Metric threads are expressed in terms of pitch, while imperial and American threads are expressed in terms of the number of threads per inch – this is their main difference. Metric threads have an equilateral tooth profile at 60 degrees, imperial threads have an isosceles tooth profile at 55 degrees, and American threads also have a 60-degree tooth profile. Metric threads use metric units, while imperial and British threads use imperial units. Pipe threads are primarily used for connecting pipes; their internal and external threads fit tightly together, and there are two types: straight pipes and tapered pipes. The nominal diameter refers to the diameter of the pipe being connected; obviously, the major diameter of the thread is larger than the nominal diameter. 1/4, 1/2, 1/8 are the nominal diameters of imperial threads, measured in inches. Thread types can be classified according to their intended use: 1. International Metric Thread System: The thread standard adopted in China’s **CNS standard. The tooth top is flat, making it easy to machine, while the tooth bottom is arc-shaped to increase the strength of the thread. The thread angle is 60 degrees, and the size is indicated by M. Male threaded connections can be divided into coarse thread and fine thread types. The notation is such as M8x1.25. (M: code, 8: nominal diameter, 1.25: pitch). 2. American Standard Thread: Both the top and bottom of the thread are flat, resulting in better strength. The thread angle is also 60 degrees, and the specification is indicated by the number of threads per inch. Such threads can be divided into coarse thread (NC) ； Fine tooth (NF) ； Ultra-fine tooth (NEF) grade 3. The notation is like 1/2-10NC. (1/2: Outer diameter ； 10: Teeth per inch ； NC code). 3. Unified Thread: Developed jointly by the United States, the United Kingdom, and Canada, it is the commonly used imperial thread at present. The thread angle is also 60 degrees, and the specification is indicated by the number of threads per inch. Such threads can be divided into coarse thread (UNC) ； Fine thread (UNF) ； Ultra-fine tooth (UNEF). The notation is such as 1/2-10UNC. (1/2: Outer diameter ； 10: Teeth per inch ； UNC code) 4. Sharp V Thread: The top and root are both sharp-shaped; it has relatively low strength and is not often used. The thread angle is 60 degrees. 5. Whitworth Thread: The thread standard adopted in the UK. A thread angle of 55 degrees is indicated by the symbol “W”. Applicable to manufacturing by rolling method. The notation is such as W1/2-10. (1/2: Outer diameter ； 10: Teeth per inch ； Code W). 6. Round thread (Knuckle Thread): A standard thread defined by the German DIN standard. Suitable for connecting light bulbs and rubber hoses. The symbol representing it is “Rd”. 7. Pipe Thread: A thread used to prevent leaks, commonly employed for connecting pipes carrying gases or liquids. The thread angle is 55 degrees; it can be divided into straight pipe threads denoted as “P.S.” and “N.P.S.”, and inclined pipe threads denoted as “N.P.T.”. The taper is 1:16, which is 3/4 inch per foot. 8. Square Thread: It offers high transmission efficiency, second only to ball screws; however, it cannot be adjusted using nuts after wear, which is its drawback. Generally used for the screws of vices and the threads of cranes. 9. Trapezoidal Thread: Also known as Ackermann thread. The transmission efficiency is slightly lower than that of square threads, but it can be adjusted using a nut after wear. The thread angle is 30 degrees in metric system and 29 degrees in imperial system. Generally used for lead screws in lathes. The symbol is represented as “Tr”. 10. Buttress Thread: Also known as oblique thread, it is suitable only for one-way transmission. Such as screw jacks, press machines, etc. The symbol is represented as “Bu”. 11. Ball screw: It is the screw type with the best transmission efficiency, but it is difficult to manufacture and extremely costly, hence it is used in precision machinery. Such as the lead screw in CNC machine tools. Notation for imperial bolts: LH 2N 5/8 × 3 - 13 UNC━ 2A. (1) LH denotes left-hand threading (RH denotes right-hand threading, which can be omitted). (2) 2N double-thread. (3) 5/8 inch imperial thread, outer diameter 5/8 ». (4) 3 Bolt length: 3”. (5)13: 13 threads per inch. (6) UNC unified standard coarse thread. (7) Grade 2 fit, external thread (3: tight fit ； 2: Moderate coordination ； 1: Loose fit) A: External thread (can be omitted) B: Internal thread. Imperial threads: The size of imperial threads is usually indicated by the number of threads per inch along the thread, commonly referred to as \"threads per inch,\" which is equal to the reciprocal of the pitch. For example, a thread with 8 teeth per inch has a pitch of 1/8 inch.