Professional screw fastening of wood construction screws

2. Insertion torque and breaking torque

The characteristic insertion torque (screw-in torque) depends on various factors, including screw type, wood type, pre-drilling and installation conditions.

Guideline values for screws with a diameter of 8 mm:

• Partially threaded screw:
  • approx. 13 Nm insertion torque
  • approx. 22 Nm characteristic breaking torque
• Fully threaded screw:
  • approx. 15 Nm insertion torque
  • approx. 28 Nm characteristic breaking torque

3. Axial load-bearing capacity of the screw shaft

The tensile load-bearing capacity also depends on the type of screw. Under standard conditions, the following guide values apply for a diameter of 8 mm:

• Partially threaded screw: approx. 20 kN
• Fully threaded screw: approx. 25 kN

➔ These values assume complete thread anchoring and a professional screw-in depth.

4. What are the consequences of incorrect screw-in depth?

Screwing pan head screws in too deeply can have several safety-related consequences:

• Increased screw-in torque: The required screw-in torque can almost double.
• Exceeding the permissible breaking torque: There is a risk of screw failure due to shearing of the shaft or tearing off of the thread.
• Damage to the wood fibre structure: Local overloading can lead to fibre breakage.
• Uncontrolled settling: The connection may give way, leading to deformation.

These effects must be critically evaluated and avoided at all costs, especially in load-bearing or stiffening components.

Here is an example of a screw connection with installation torque (pull-out torque)