When deciding what size or type of fastener best fits your needs, it is important to know the strength of the fasteners you’re choosing from. This can identified by the grade or property class associated with the fastener. Inch fasteners, which are more common in North America, will have a grade or a rating from the American Society for Testing and Materials. Property classes are used for metric fasteners.
In the metric system, property classes are used to break down the strengths of different fasteners. Each class was created using a combination of two numbers. The first number in this combination is representative of the approximate tensile strength of the fastener, multiplied by 100 in metric units of MPa. The second number, which follows the decimal point, is used to determine yield strength. This is approximated by multiplying that percentage number by the tensile strength of the fastener.
For example, if the property class of a fastener is 10.9, the tensile strength is approximately 1000 MPa. The yield strength would be 90% of this, or 0.9 multiplied by 1000, which equals out to 900. This is the most distinct difference between grades and property classes, because grades do not utilize a similar number convention.
For instance, Grade 2 is considered low strength, Grade 5 medium strength and Grade 8 high strength. Due to the wide variety of grades and the fact that fasteners all tend to look similar, strength grades for medium carbon and alloy steel can often be marked for identification. This is more important to look out for if strength is a determining factor for you.
There are charts available for identifying what each grade or class means, so be sure to reference those when using strength as a factor in your purchase. To learn more about grades and property classes for fasteners, contact Bossard at ProvenProductivity@bossard.com.
Property Class Versus Grades by Bossard