Wedge washers (DIN 6798, DIN 6907)

Wedge washers (DIN 6798, 6907) are mechanical securing elements with limited spring and locking action. They do not provide standard-compliant protection against loosening, and the required residual spring force specified in DIN 267-26 is not achieved. Their use is permitted only for screws with a strength class of ≤ 5.8; they are unsuitable for electrical connections. The standards were removed in 2004. Modern alternatives, such as NSK washers, are technically superior and comply with standards.

  1. Design and Function
    Fan-shaped washers are mechanical screw-locking elements made of spring steel with radially arranged cutting edges. Their function is based on a slight spring effect as well as on the locking engagement of the edges with the mating surface.
    They were used to prevent loosening under dynamic loads and also for making contact with coated components. A permanent locking effect or a defined residual spring force according to DIN 267-26 is not achieved, which is why they no longer represent the state of the art.
  2. Principles of Operation
    1. Axial spring effect:
      Elastic deformation during tightening creates a slight preload, which generates frictional locking.
    2. Positive-lock locking effect:
      The cutting edges, by engaging with the surface, create a restraining effect against back-rotation, but without a defined depth of engagement or repeatability.
  3. Application Limits
    1. Use only for low property classes (max. 5.8)
    2. Limitations with A4 stainless steel due to reduced elasticity
    3. Not suitable for electrical glands: no defined contact zones, increased risk of corrosion
    4. Surface damage may occur on coated components
    5. Combination with flat washers increases settling and further reduces functionality
  4. Advantages
    1. Cost-effective to manufacture
    2. Easy to use
  5. Disadvantages
    1. No proven locking effect; placebo effect
    2. Surface damage caused by cutting edges
    3. Variation in assembly force due to fluctuations in the coefficient of friction
    4. No protective effect in case of overloading
    5. No reliable electrical contact in electrical applications
    6. Risk of increased corrosion combined with insufficient spring effect
  6. Normative Classification
    The DIN 6798 and DIN 6907 standards were removed in 2004 because they do not provide the required technical safety.
    Fan-shaped washers are no longer considered to comply with standards; their use must be evaluated critically from a liability perspective.
  7. Design Guidelines and Recommendations
    Fan-shaped washers do not meet the requirements of modern screw locking devices and are not recommended—especially not in safety-critical or function-critical applications.
    Modern alternatives such as NSK washers (types E/EL for electrical applications, S/M/L for mechanical applications) offer a combined spring and locking effect, comply with DIN 267-26, and meet the requirements for safety, repeatability, and material protection.

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