Fixings experience different load directions: the different forces are, tensile, shear and diagonal. There can also often be a combination of two force directions e.g. resulting in diagonal tension (Fig. 1). Force directions are not always fixed, but can also change during the length of use. 

A fixing must be able to conduct the forces occurring securely into the anchor base.  In modern fixing technology, three different bearing mechanisms are used: friction fit, positive fit and adhesive bond or a combination of these. (Fig. 2 to 4).

 
     
  Fixing loads:
Various forces can have an effect on a fixing. There are three load directions: in an axial direction: tensile force (Z) or pressure; vertically: shear force (Q); and also diagonal force (R), resulting from tensile and shear force.
     
  Friction fit:
In the case of friction fit, the expanded fixing is pressed against the drill hole wall and the load is absorbed by friction.

 
     
  Positive fit:
In the case of positive fit, the fixing adapts itself in its geometry to the form of the substrate or drill hole.
     
  Adhesive bonding:
Adhesive bonding connects a fastening element to the substrate through mortar or resin.

The term „working load” is used to describe the respective load bearing values.  It is given in kilo Newton (1 kN = 1000 N ≈ 100 kg).

The working loads given, lie clearly under the  "breaking load value" due to a safety factor being taken into account. This value denotes, under laboratory conditions, masonry failure, screws breaking, or the fixing being pulled out of the hole.  

When choosing the correct dowel, one must ensure that the non-loadbearing layer (eg plaster, tile, etc, ) does not count towards the anchoring depth.

The screws should always have the largest possible diameter, in respect of the fixing, in order to attain maximum hold.

The screw length  = length of fixing + thickness of object to be mounted + 1x screw diameter. The result is then rounded up to the next standard screw length (Fig. 5). With the aid of our interactive calculating tool, these values can also be determined immediately online.

 
     
  Correct rates:
1. Drill hole depth = B (fixing length) + 10 mm,
2. Screw length = A (screw diameter) + B + C (object to be mounted),
3. Drill diameter = Fixing diameter  

Description:
D = non load-bearing slice (coating or plaster)
E = screw length
hef = Effective anchorage depth
     
  Minimum distances:
of plastic plugs depend on the building material und anchorage depth (hef).

In order to avoid overloading building materials, rules determine the distances of the fixings to each other, or to the edge of the building materials. More on this in the section about distances.