Screws may look unassuming, but their performance depends on one crucial specification: the property class. It indicates how much tensile force a screw can withstand and at what point it begins to permanently deform. This knowledge is particularly important in mechanical engineering, steel construction, and industrial plant engineering.

How Do You Read a Property Class?

Let’s take property class 12.9 as an example:

First number (12)
Multiplying it by 100 gives the tensile strength:
→ 12 × 100 = 1,200 N/mm²
This is the maximum stress the material can withstand before it breaks.

Second number (9)
This describes the ratio of yield strength to tensile strength:
→ 90% of 1,200 N/mm² = 1,080 N/mm²
Up to this value, the screw returns to its original shape after the load is removed.

Key takeaway: The higher the numbers, the higher the load-bearing capacity—but also the greater the requirements for installation and design.

Common Property Classes at a Glance

Property Class 5.6

-Tensile strength: approx. 500 N/mm²

-Yield strength: approx. 300 N/mm²

-Applications: simple structures, wood construction, or lightweight construction

-Advantage: forgiving and easy to install

Property Class 8.8

-Tensile strength: 800 N/mm²

-Yield strength: 640 N/mm²

-Applications: mechanical engineering, steel construction, vehicle engineering

-The industry standard for many applications

Property Class 10.9

-Tensile strength: 1,000 N/mm²

-Yield strength: 900 N/mm²

-Applications: highly loaded bolted joints, e.g., in industrial plant and vehicle engineering

-High preload forces possible; precise installation required

Property Class 12.9

-Tensile strength: 1,200 N/mm²

-Yield strength: 1,080 N/mm²

-Applications: extreme mechanical loads

-Maximum strength with relatively low elongation

How Much Load Can Screws Really Withstand?

In addition to the property class, load-bearing capacity also depends on the diameter.
An M64 screw in property class 10.9, when properly designed, can withstand loads well in excess of 100 metric tons. That is roughly equivalent to the weight of a small aircraft. 💥

Conclusion:
Screws are small components with enormous responsibility. The right property class determines the safety, service life, and functionality of entire structures—and is therefore an essential factor in modern engineering.