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.

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                                                                                                      Written by

Mr.Nuttapol Sirilert

International Sales team

Hanshin Neji Co.,Ltd