Bolt grades refer to the strength of a bolt. Bolt is a kind of fastener consisting of a head at one end and a threaded shaft at the other end. The factors determining the strength of the bolt depend on the manufacturing material and the process it undergoes.
Bolt grades are standardised by organisations such as the Society of Automotive Engineers (SAE) and the International Organization for Standardization (ISO).
The grading systems for bolts depend on the industry’s use. The most common ones are the SAE system for bolts used in automotive applications and the ISO system for bolts in general engineering applications.
SAE Bolt Grade System
The SAE system uses grades such as Grade 2, Grade 5, and Grade 8 to classify bolts according to their strength.
Grade 2 bolts are made of low-carbon steel and are the weakest. They are suitable for light-duty applications such as attaching brackets or sheet metal to wood.
Grade 5 bolts, on the other hand, are made of medium-carbon steel and are sturdier than Grade 2 bolts. They are suitable for applications such as attaching brackets to metal or attaching engine parts.
Grade 8 bolts are the strongest because of the use of high-carbon steel in manufacturing. They are suitable for heavy-duty applications such as attaching load-bearing parts or joining parts subject to high stress.
ISO Bolt Grade System
The ISO system uses designations such as 8.8, 10.9, and 12.9 to classify bolts according to their strength.
These designations refer to the minimum tensile strength of the bolt, with 8.8 grade meaning that the bolt has a minimum tensile strength of 800 MPa. The 10.9 grade means the bolt has a minimum tensile strength of 1000 MPa, and so on. The higher the number, the stronger the bolt.
Factors to Consider
Bolt grade is a predominant factor when choosing bolts for any industrial application. Using a bolt that is too weak can lead to failure while using a bolt that is too strong can be unnecessarily expensive. High-strength bolts can cause problems due to the high clamping force it generates.
In addition to the manufacturing material and process, other factors that can affect the strength of a bolt include the size of the bolt, the type of thread, and the surface finish.
The size of the bolt refers to its diameter and length, with larger bolts generally being stronger than smaller ones.
The type of thread, such as fine or coarse, can also affect the strength of the bolt.
Finally, the surface finish, such as galvanising or plating, can affect the corrosion resistance and, therefore, the overall strength of the bolt.
Concluding Thoughts
In conclusion, bolt grades refer to the strength of a bolt and are determined by the material it is made of and the manufacturing process it undergoes. It is important to use the correct bolt grade for the application to ensure that the bolt is strong enough to handle the loads it will be subjected to. If you have any doubts related to the bolt grade and which bolt to choose, you can contact us. We have been in the fastener manufacturing business for the past 25 years, and our experts have in-depth knowledge of what they are manufacturing.
