What does number on the fasteners’ head mean?

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What does number on the fasteners’ head mean?

     Hi everyone, here we go again! This issue we will talk about Strength of Fasteners or fasteners class in term of general use.

    Have you ever curious what does numbers 4.8, 8.8, 10.9 or 12.9 on the Fasteners head which generally using in manufacturing industry and general usage refer to?  Today we will clarify this issue and make good understanding for you.

These numbers are mostly shown on Metric fasteners’ head according to ISO or JIS standard. If there are Imperial sizes or different standard such as SAE or ASTM, it might be differently shown as Slash Line (3, 5 and 6 lines on fasteners head). By the way, this issue we will explain only the numbers shown on ISO and JIS standard.

The numbers which are written as 4.8, 8.8, 10.9 or 12.9 refer to Tensile Strength on the first digit and Yield Strength on the second digit to make users be able to choose the right fasteners that fit to the application.  Please see detail as below.



4.8 Hexagon bolt

    Number 4 of from the first digit, refers to Tensile Strength of the particular fasteners that be able to bear with the maximum load. We can know how much it can bear by taking the first digit number X (multiply) with 100, and we will get the result of how much this fastener can withstand. Result will be in Mpa (Megapascals), N/mm2 (Newton/Square Millimeter) or Psi (Pound/Square Inch) depending on the standard or country of usage but these formats can be convert to each other

For example : Tensile Strength = 4 x 100 = 400 Mpa or N/mm2

    Number 8 on the second digit, refers to Yield Strength that this fastener can bear and remain full function of usage before it will be permanent deformation. We can know how much it can bear by taking result of the Tensile Strength from the number in the first digit   X (multiply) with 0.8 (from number 8 or different number on second digit), and we will get the result of how much this fastener can bear and remain full function of usage. Users must concern on this strength as well to prevent broken or misuse of fasteners.

For example : Yield Strength  = 400 x 0.8 = 320 Mpa or N/mm2

In summary, 4.8 class fasteners will have Tensile Strength = 400 N/mm2 and Yield Strength = 320 N/mm2

So the 8.8 class fasteners will have this following result, Tensile Strength = 800 N/mm2 and Yield Strength = 640 N/mm2

    The result from this formula is just for a reference only, practically it may vary depends on application factors like heat or surface condition. So, users must carefully concern of affected factor which cause to the application as well.



    For the first English letter or other symbols on the fasteners head for example the text: KKT, KN or others, they are identifying maker name or trademark. There are no strictly rule to state these maker name or trademark on the fasteners head, it’s depending on maker standard. KKT mark as above is stand for the maker name: KYOKUTO SEISAKUSHO CO., LTD.

There are some more example of application and explaination of 4.8, 6.8, 8.8, 10.9, and 12.9 hexagon bolt as below.

4.8 Hexagon bolt is one of the most common fasteners in the world due to its universal applications. This bolt has a hexagon shaped head, which mostly fasten with spanner or hexagon wrench that most of household might have, so it is easy for everyone to use. Due to 4.8 hexagon bolt is low-tensile strength fasteners, make it suitable for light weight application which can be using indoor or outdoor use as well, plating will be vary due to each application.

How to use? : The place or area must be pre-tapped with your desired dimension, then use hexagon wrench or spanner to install them with proper torque. Also, even without pre-tapped hole, it can be used with non-threaded hole as well. This application will hang the bolt and fasten with female nut and the end.

Where to use, what kind of business using this product? : Due to its low tensile strength make 4.8 class Hexagon bolt hold Tensile Strength = 400 N/mm² and Yield Strength = 320 N/mm² This strength suit for light weight application such as furniture assemble, cabinet assemble, light steel works and etc. Generally, you can see this bolt as a very common fasteners in your daily life. Even when you are sitting at the bench in the park and look underneath, you might find this 4.8 Hexagon bolt.

 

6.8 Hexagon Bolt's appearance look like other standard hex bolt which is one of the most common fasteners in the world due to its universal applications. This bolt has a hexagon shaped head, which mostly fasten with spanner or hexagon wrench. This is mid-tensile strength bolt which mostly available in larger sizes. This is rare bolt that you might not see it often.


How to use? : The place or area must be pre-tapped with your desired dimension, then use hexagon wrench or spanner to install them with proper torque. Also, even without pre-tapped, it can be use with non-threaded hole as well. This application will hang the bolt and fasten with female nut and the end. 6.8 Hexagon bolt may use with higher tensile application than 4.8 Hexagon bolt.

Where to use, what kind of business using this product? : Due to its mid-tensile strength make 6.8 class Hexagon bolt hold Tensile Strength = 600 N/mm² and Yield Strength = 480 N/mm² This strength suit for medium weight application such as assemble with machine or general application with and etc. Normally, this is a rare bolt which mostly made by order only, so there might be a low chance for you to see this bolt in your daily life.


8.8 Hexagon Bolt is one of the most common screw in the world due to its universal applications. This is upgraded version of 4.8 hex bolt which mostly use with high-tensile application. This bolt also has a hexagon shaped head, which mostly fasten with spanner or hexagon wrench. This is 8.8 high-tensile strength hex bolt mostly available from M6 due to material strength restriction.

How to use? : The place or area must be pre-tapped with your desired dimension, then use hexagon wrench or spanner to install them with proper torque. For high-tensile bolt, torque is a concerned factor that user must fasten them properly.

Also, even without pre-tapped, it can be use with non-threaded hole as well. This application will hang the bolt and fasten with female nut and the end, if it will be using with female nut, the nut strength must be 8T grade or equivalent.

Where to use, what kind of business using this product? : Due to its high-tensile strength make 8.8 class Hexagon bolt hold Tensile Strength = 800 N/mm² and Yield Strength = 640 N/mm² This strength suit for high weight application such as assemble with general machine, conveyor, warehouse equipment or any general application that torque or high tensile are concerned. Normally, you might not able to see this bolt in public so much, they are mostly visible in factory or machine.

 

10.9 Hexagon bolt may look similar to other common hexagon bolts and its versatility makes this bolt to be one of the most common fasteners in the world. The head of this bolt is hexagonal, and it is mainly fasten by using a spanner or a hexagonal wrench. This bolt has high tensile strength and mainly available in large sizes only. Since it is a bolt that is often used for high-strength application, there are various sizes, and bolts with a fine pitch are often used, making it a highly versatile bolt among high-strength bolts.

How to use? : Tap the desired dimensions in advance, and use a hexagon wrench or spanner to install with the proper torque. It can also be used without taps other than screw holes. It is also possible to insert a bolt into a hole without a tapped hole and tighten the tip with a nut.
 
Where and what kind of work is this product used for? : High-strength bolts mainly used for construction machinery and machinery. The material is SCM435.
The maximum tensile strength is 1040n/mm. Yield strength is 936N/mm at 90% of maximum tensile. The type of plating is basically black oxide, and in addition, we also have Unichrome and Trivalent Zinc plating 10.9 Hexagon Bolt in stock.

*One thing to keep in mind is that if you're going to Electro-galvanizing plating with 10.9 Hexagon bolt, you have to bake it to remove hydrogen out of the bolt to prevent Hydrogen embrittlement*

12.9 Hexagon bolt has mark indicates the strength classification, the tensile strength is 1,200N/㎟, the proof stress at 0.2% which is Yield strength 1,080N/㎟
It has a tensile strength of 1,200N/㎟, which means that it will not break up to 1200N/㎟, and have a yield strength at 1,080N/㎟, this yield strength means if tensile is within 1,080N/㎟ it will remain it’s flexibility to return itself into original state after being stretched.

The surface treatment mostly be black oxide, the material is structural alloy steel (SCM435) which hardness is around 38-43HRC


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                                                                                                      Written by

Mr.Nuttapol Sirilert

International Sales team

Hanshin Neji Co.,Ltd