Bolt Grades – What is It? What you should know about it

Bolts. What are they?  These are the components which are also referred to as fasteners and are used to hold two objects firmly together.  There are certain things that are very crucial to consider while selecting the right bolt for an application. These factors include shape, size, thread type, length, material, coating, classes of fit, and grade. Except for grade, all these factors have been discussed quite extensively.  Bolt grade is one of the important factors that is often ignored. What are the grades?  What makes this factor so important in selecting the right bolt? Read the following post to find answers to this question.

What does a Bolt Grade Mean?

This is the most basic question for someone who is not familiar with this term. This is a technical term which determines the properties of a bolt. The grade of a bolt determines the maximum amount of stress that the bolt can handle. It also helps determine which tools are suitable for tightening these bolts. Moreover, the type of method used for tightening the bolt is also dependent upon the grade of the bolt. Therefore, it is very important to understand the grade of a bolt in order to use it properly.

What are the Different Bolt Grades?

There are a huge variety of bolt grades that are suitable for a diverse range of applications and environments. Let us have a look at each grade and its properties:

  1. Grade 2 – The grade 2 bolts are most commonly manufactured from low or medium carbon steel. Bolts of this grade do not have any radial lines. The bolts of this grade with a nominal size range from 1/4″ to 3/4″ have a minimum tensile strength of about 57000 psi and the yield strength of sizes from 3/4″ to 1/2″ 36000 psi.
  2. Grade 5 – Unlike grade 2 bolts, grade 5 bolts feature 5 radial lines. These bolts are manufactured from medium carbon steel. These bolts come in two different size ranges – 1/4″ to 1″ and 1″ to 1 1/2″, which have the proof load of 85000 psi and 74000 psi respectively.
  3. Grade 8 – Grade 8 bolts are made from medium carbon alloy steel. The bolts of this grade feature 6 radial lines. The nominal size of the grade 8 bolts can be from 1/4″ to 1 1/2″. The minimum yield strength of this grade bolt is 130,000 psi. A maximum of 120,000 psi of tensile force (proof load) can be applied to grade 8 bolts.
  4. Grade S – Grade S bolts have the capability to withstand 45 to 49.9 MT of stress per 6.45 cm3. Bolts of this grade are heavy duty bolts that are strong and highly durable, and thus are used in a variety of heavy duty applications.

Other than those explained above, there are various other grades of bolts, which include grade R, metric 8.8, metric 10.9, etc. Having a good understanding of these grades goes a long way in selecting the right type of bolt for an application. However, the supplier from whom you buy the bolts is also important if you are looking for good quality products for different applications. There are very few companies like Norwood Screw Machine Parts who have been supplying quality bolts for a varied range of applications and industries for close to 60 years.

About Norwood Screw Machine

Norwood is a privately owned custom screw machine parts manufacturer. For over 59 years we serve some of the largest corporations to the small company with a new product to develop. Whether a unique item with a one time requirement or a long running contract order with scheduled deliveries, Norwood Screw Machine Parts is the right choice for the job.



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