Tensile strength is the mechanical property most widely associated with standard threaded fasteners. Metric Fasteners come in variety of strength, the grade ranging from 4.8 to 6.8, 8.8, 10.9 and 12.9.

Let’s discuss the strength grades of metric fasteners today.

Grade4.8 Tensile strength is 400Mpa.

The tensile strength is equivalent to the strength of  low carbon steel after cold hardening deformation.

The minimum elongation of physical fastener is Af ≥0.24.

Remark: After cold hardening deformation, brittleness higher, toughness lower.
Grade6.8 Tensile strength is 600Mpa.

Medium carbon steel can be manufactured by cold heading process.

The minimum elongation of physical fastener is Af ≥0.20.

Remark: After cold hardening deformation, brittleness higher, toughness lower.
Grade 8.8 Tensile strength is 800-830Mpa.

It needs to be produced with medium carbon steel or alloy steel, and must be heat treatment.

Remark: High strength after heat treatment but beware of brittleness.
Grade 10.9 Tensile strength is 830-1040Mpa.

The fasteners needs to be produced with alloy steel material, and must be heat treatment.

Remark: High strength after heat treatment but beware of brittleness.
Grade 12.9 Tensile strength is 1200Mpa.

The fasteners needs to be produced with alloy steel material, and must be heat treatment, but it needs to consider the risk of stress.

Remark:High strength after heat treatment but beware of brittleness.