Nut grade and classification
Nut grades cover various forms, such as ordinary, non-standard, old national standard, new national standard, American standard, British standard, German standard and other different standards. In addition, nuts are classified into Type I, Type II, and Thin types based on their nominal thickness. It should be noted that nuts above level 8 are specifically divided into two types: Type I and Type II.
>Application of Type I and Type II Nuts
In terms of application, I-type nuts are highly praised for their wide applicability. It is further divided into three levels: A, B, and C. Grade A and B nuts are suitable for machines, equipment, and structures with high precision and surface quality, while grade C nuts are suitable for situations with lower requirements for precision and surface quality. In contrast, Type II hex nuts have a thicker thickness and are commonly used in situations that require frequent assembly and disassembly.
>Guidance on National Standards
In addition, a series of national standards specify the specific dimensions and performance of nuts, such as GB41, GB6170, etc., covering different types and grades of nuts. These standards provide important references for the selection and use of nuts.
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Matching use of bolts and nuts
>Metric bolt and nut grades
The grade range of metric bolts is wide, including 4.6, 4.8, 5.8, 6.8, 8.8, 9.8, 10.9, and 12.9. Similarly, metric nuts have different grades, such as 4, 5, 6, 8, 10, and 12, among which 4 and 5 specifically refer to the strength grade of thin nuts.
>Flexibility and considerations for level coordination
So, how to match the grades of bolts and nuts?
Generally speaking, the strength grade of bolts and nuts should be consistent. For example, if 8.8 grade bolts are selected, 8-grade nuts should be used. However, considering the actual usage situation, if it is difficult to replace the nut but easy to replace the bolt, the combination of bolt 4.8 and nut 5 can also be flexibly adjusted.
In some application scenarios, the strength design of nuts may be slightly lower than that of bolts, which is not an arbitrary action. The main consideration is that bolt failure is often concealed and sometimes even sudden, while nut failure is relatively easier to detect. This design difference aims to ensure that the lifespan of screws can exceed that of nuts when used together, thereby reducing costs and simplifying operations when disassembling and replacing fasteners.
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