Bolting Property Classes 8.8 10.9 12.9 & 14.9
Have you ever stopped to think what the carbon steel bolting grade numbers signify. They’re not just random digits used to identify a material grade. These grade are stipulated in various international standards including DIN 267 and ISO 898. The specific detail should be verified from the required standard directly but as a general guide this feature will assist.
The symbol for the property classes of hex bolts, screws and studs consists of two numbers separated by a decimal point. 8.8, 10.9, 12.9, 14.9 etc.
Take the whole number before the decimal point. This number, when multiplied by a hundred, gives you the nominal tensile strength in newtons per millimetre squared.
The digit following the decimal point, multiplied by ten, gives you the yield stress ration, or the percentage ratio between the lower yield stress and the nominal tensile strength.
If you now multiply the first number by 10 times the second number you will arrive at the notional yield stress in newtons per millimetre squared.
The main characteristic property of Nuts is the thread stripping strength (proof stress).
The property classes of nuts are designated by a number which indicates the maximum appropriate property class of bolt with which they should be fitted. Therefore nut property classes are the same as the bolt designation initial number.
Internationally, mechanical stress is expressed in newtons per square area, in bolting N/mm2. Common practise overseas is to use the unit megapascal (MPa), which corresponds directly to N/mm2.
For example 1,200 N/mm2 = 1,200 MPa
An example using a hex bolt with property class 10.9
The Nominal tensile strength of a 10.9 bolt is calculated
10 x 100 = 1,000 N/mm2 (MPa)
The Yield stress ratio 9 x 10 = 90%
The Yield stress is therefore
90% of 1,000 = 900 N/mm2 (MPa)
Bolts and Studs can be supplied in Property classes
Grade 3.6
Grade 4.6
Grade 4.8
Grade 5.6
Grade 5.8
Grade 6.8
Grade 8.8
Grade 9.8
Grade 10.9
Grade 12.9
Grade 14.9
Nuts Property classes
Grade 6
Grade 8
Grade 9
Grade 10
Grade 12
Grade 14
Nuts of a higher property class can normally be used in the place of nuts of a lower property class.
* Property classes 14.9 are not detailed in the ISO or ANSI standards.
