Spring rings in accordance with DIN 127, 128, 6905, and 7980
Spring rings conforming to DIN 127, 128, 6905, and 7980 do not adequately prevent the spontaneous loosening of bolted connections and are considered technically unsuitable under current standards. The required residual spring force specified in DIN 267-26 is not achieved, which can lead to placebo effects, unreliable preload, and surface damage. Their use is no longer permitted by standards. It is recommended to replace them with modern securing elements such as the NSK washer.
- Definition, Purpose, and Suitability
Spring rings are mechanical screw-locking elements that were originally designed to prevent the spontaneous loosening of screw connections under dynamic loads (e.g., vibration, shock). They do not provide a standard-compliant locking effect against self-acting loosening by rotation or loosening in accordance with the current state of the art. In particular, the required residual spring force according to DIN 267 Part 26 is not achieved, which is why their use is considered unsuitable.
- Design and Function
- Axial spring effect:
When tightened, the spring ring is elastically deformed and generates a slight additional preload. This is intended to increase frictional engagement and delay loosening.
- Wedge/locking effect (Forms A/B only – DIN 127):
The open or curved geometry creates a slight mechanical stress during relative rotational movement, which is intended to slow down back rotation. However, this effect is unreliable and cannot be validated in accordance with standards.
- Application Limits and Typical Uses
Spring rings are typically used only in combination with low-strength screws (≤ property class 5.8).
When used with A4 stainless steel, elasticity is significantly reduced, which further limits their effectiveness.
Spring rings are not suitable for electrically conductive connections.
When used in combination with flat washers to protect surfaces, additional settling may occur, along with an increased susceptibility to loosening.
- Advantages
- Low cost compared to modern securing elements
- Disadvantages
- No standard-compliant locking effect
- Risk of a placebo effect (apparent locking without technical function)
- Damage to mating surfaces during direct application
- Variation in assembly preload forces due to unstable friction conditions
- No protective effect in the event of overloading
- Combined use with flat washers leads to increased settling
- Standard Classification
The standards DIN 127, DIN 128, DIN 6905, and DIN 7980 were removed in 2004 because they do not provide the required technical locking effect.
Spring rings are no longer considered state-of-the-art.
Their use may have liability implications—therefore, an assessment of their admissibility is required.
- Design Guidelines
The use of spring rings is not recommended from a technical or legal standpoint.
Even when used in combination with flat washers, they do not provide sufficient locking effectiveness.
It is recommended to replace them with modern screw locking elements, e.g., NSK washers, which prevent both slackening and unscrewing and comply with DIN 267-26. NSK-E / NSK-EL are suitable for electrical applications, while the S, M, and L variants are suitable for mechanical connections.
Back to the glossary overview
DIN 267-26
"Mechanical fasteners—Technical delivery conditions—Part 26: Spring steel locking washers for bolted joints" specifies requirements for conical spring steel locking washers designed to compensate for a loss of preload due to embedding or creeping. It specifies materials, hardness (420–490 HV), surface finishes, test methods (e.g., embedding, endurance, and spring force tests), as well as packaging and marking. The standard ensures the quality and functional reliability of the washers.
Loosening
Self-acting loosening by rotation refers to the rotational movement of a screw or nut without an external torque load, resulting from the loss of preload and anti-slip strength, preceded by slackening and triggered by dynamic transverse loads. The self-loosening mechanism proceeds in several phases—beginning with relative rotational movements and bending stress (Phase 1), through thread slippage and head tilting (Phase 2), to rotation caused by stored torsion (Phase 3), and finally to complete loosening due to loss of friction (Phase 4). To ensure safety, securing elements such as anti-loosening elements or multifunctional locking elements such as NSK® washers are required; in addition to preventing loosening, these elements also increase slip resistance and resilience, thereby improving overall resilience—especially with short clamping lengths.
Electrically Conductive Connections
Electrically conductive screw connections ensure low-resistance transfer of current while providing mechanical strength, even through insulating layers. The NSK-K contact washer combines electrical conductivity, spring action, and anti-loosening protection—ideal for earthing and equipotential bonding. See also NSK-E Technical Report.
NSK Washers
NSK washers are one-piece, multifunctional screw-locking elements that provide both a force-fit and a form-fit to prevent slackening and unscrewing. They increase elastic resilience and anti-seize properties; up to property class 12.9, they are also suitable for electrically conductive connections (earthing & electrical potential equalisation) as well as electrical contact glands, and comply with various standards, such as DIN EN 17976, DIN 25201, DIN 50343, and DIN 267 Part 26; they are considered state-of-the-art and offer assembly-friendly, standards-compliant, and cost- and weight-efficient solutions.
Slackening
First, the slackening phase occurs in the slackening mechanism of bolted joints. During slackening—or in the slackening phase of bolted joints—the preload force decreases due to embedding, relaxation, and creeping. The sliding resistance is maintained, so that operational forces continue to be transmitted through clamping. Embedding occurs through the plastic leveling of rough surfaces immediately after assembly. Relaxation and creeping lead to further force reduction over the long term. Screw connections can be secured against slackening using special screw locking elements or multifunctional screw locking elements.
