Inch bolts and GB bolts are fasteners under two different standard systems, which are widely used in machinery manufacturing, construction engineering, automobile industry and other fields. Although they are similar in function, there are significant differences in size specifications, thread standards, strength levels and other aspects. The following is a detailed comparison between imperial bolts and national standard bolts in many aspects. 1. Standard system - British bolts: British bolts use imperial units (inches, pounds, etc.), mainly following the British Standard (BS), the United States standard (ANSI/ASME) and so on. British bolt size, thread specifications and strength level is usually expressed in inches. - National standard bolts: National standard bolts use metric units (millimeters, kilograms, etc.), mainly following the Chinese national standard (GB). The dimensions, thread specifications and strength grades of GB bolts are expressed in millimeters. 2. Thread specifications - Inch bolts: The thread specifications of inch bolts are usually expressed in terms of the number of threads per inch (TPI, Threads Per Inch), e.g., 1/4-20 means that the diameter is 1/4 inch and there are 20 threads per inch. Inch threads are commonly available in two types: UNC (coarse thread) and UNF (fine thread). - National standard bolts: The thread specifications of national standard bolts are expressed in terms of metric threads, for example, M6 indicates a metric thread with a diameter of 6 millimeters. There are two common types of national standard threads, coarse thread and fine thread, coarse thread is usually used for general connection, fine thread is used for occasions that require higher precision.
3. Dimensional specifications
- British bolts: British bolt size specifications in inches, common specifications are 1/4, 3/8, 1/2, 5/8, 3/4, 7/8, 1 inch and so on. The length of imperial bolts is also measured in inches, for example, 1/2 inch x 2 inches indicates that the diameter is 1/2 inch and the length is 2 inches.
- National standard bolts: the size of the national standard bolt specifications in millimeters, common specifications are M4, M5, M6, M8, M10, M12, M16 and so on. The length of national standard bolts is also measured in millimeters, for example, M8×20 means that the diameter is 8 mm and the length is 20 mm.
4. Strength grade
- Inch bolts: The strength grades of inch bolts are usually expressed in SAE (Society of Automotive Engineers) standards, such as SAE Grade 5, SAE Grade 8, etc. These grades indicate the tensile strength of the bolt. These grades indicate the tensile strength and yield strength of bolts, and the strength of Grade 8 bolts is higher than that of Grade 5 bolts.
- National standard bolts: The strength grade of national standard bolts is indicated by GB standard, such as Grade 4.8, Grade 8.8, Grade 10.9, Grade 12.9, etc. These grades indicate the tensile strength and yield strength of bolts, and the strength of Grade 8 bolts is higher than that of Grade 5 bolts. These grades indicate the tensile strength and yield strength of the bolts, and the larger the value, the higher the strength. For example, the tensile strength of 8.8 grade bolts is 800MPa and the yield strength is 640MPa.
5. Field of application
- Inch bolts: Inch bolts are widely used in the United States, the United Kingdom and other countries and regions that use imperial units, especially in the automotive, aerospace, petrochemical and other fields. Due to historical reasons, British bolts occupy a dominant position in the mechanical equipment in these areas.
- National standard bolts: National standard bolts are mainly used in China and countries and regions using metric units, and are widely used in machinery manufacturing, construction engineering, power equipment and other fields. With the rise of China's manufacturing industry, the application of national standard bolts in the international market is gradually increasing.
6. Interchangeability and compatibility
- British bolts and GB bolts: due to the different size units and thread specifications, British bolts and GB bolts are usually not directly interchangeable. For example, 1/4 inch inch bolts and M6 national standard bolts in the size of close, but due to different thread specifications, can not be directly replaced. In practice, if interchangeability is required, it is usually necessary to use an adapter or adaptor.
7. Material and surface treatment
- Inch bolts: The materials of inch bolts are usually carbon steel, alloy steel, stainless steel, etc. The surface treatments include galvanized, nickel-plated, blackened, etc. These treatments can improve the resistance of the bolts. These treatments can improve the bolt's corrosion resistance and aesthetics.
- National standard bolts: National standard bolts are also mostly made of carbon steel, alloy steel, stainless steel, etc., and the surface treatment includes zinc plating, nickel plating, blackening, Dacromet and so on. The surface treatment technology of GB bolts has developed rapidly in recent years, and part of the treatment has reached the international advanced level.
8. Price and market
- Imperial bolts: As imperial bolts are mainly used in specific regions, their prices are usually higher, especially in non-imperial countries, where prices may rise further due to higher import costs.
- National standard bolts: National standard bolts are more expensive due to the fact that they are used in