Choosing the right screw locking

Whether spring lock washer, adhesive or serrated flange: which locking method is any good can only be said once it is clear how the joint would come loose. Under static load it settles, under vibration and transverse force it self-loosens. There are separate solutions for each. And some elements that are still listed in many bills of materials have been shown not to lock at all.

Why bolted joints come loose

A bolted joint holds as long as there is enough preload in it. This force is lost in two ways, which differ in cause and remedy.

The first way is loosening through settling. Roughness on the surfaces flattens, soft materials creep, and every additional joint interface increases the amount of settling. The screw does not even have to turn for this. It already happens under static load.

With self-loosening, on the other hand, the clamped components shift against each other under dynamic transverse load. This creates an internal loosening torque that can overcome the self-locking in the thread and at the bearing surfaces. Depending on the frequency of the load cycles, the joint then loosens, and in the worst case it comes apart.

The first locking measure is therefore the design itself. Reyher's technical guide, which is based on DIN 25201-4, first recommends few joint interfaces, no unnecessary washers and no soft washers to DIN 125 under high-strength screws from property class 8.8. A locking element is only added if that is not enough.

What types of screw locking are there?

Technically, a distinction is made between anti-settling locking, anti-loss locking and anti-loosening locking. The three groups act against different types of failure and maintain different amounts of preload, as the overview shows.

Source of the percentages: Reyher, Securing bolted joints.

The decisive factor is the boundary between anti-loss and anti-loosening locking. Anti-loss locking ensures that nothing falls off. However, the joint can lose a large part of its preload in the process.

Positive and wedge-type locking

Mechanical screw locking works by positive locking. Serrations or ribs under the head or nut dig into the bearing surface. On soft materials such as aluminium or structural steel, the overall coefficient of friction rises to 0.2 to 0.3, and the tightening torque must be adjusted accordingly.

Wedge-locking washers work in pairs. Their wedge angle is greater than the lead angle of the thread. If the screw tries to loosen, the preload therefore increases instead of falling.

Clamping and adhesive locking

Clamping locking creates frictional locking in the thread, for example via a plastic coating as a patch, strip or all round. DIN 267-28 specifies what a clamping coating on steel screws must achieve. According to Reyher, they count as anti-loss locking: the joint does not come apart, but a significant loss of preload is possible.

Adhesive locking creates a material bond in the thread. In the micro-encapsulated version, capsules containing adhesive and hardener sit on the thread. They break open when the screw is tightened, the two components mix and cure. Generally, the joint is secured against loosening after 24 hours and sealed at the same time. DIN 267-27 describes this MK coating.

DIN 267-28 and DIN 267-27 compared

Both standards apply to steel screws with ISO metric thread to DIN ISO 261, but they set different limits for thread size and temperature. It is precisely these limits that are most often confused during design.

Source: DIN Media, standard pages DIN 267-28 and DIN 267-27, accessed on 26 September 2026.

Above M18, therefore, only DIN 267-27 of the two standards covers the thread. At high operating temperatures, on the other hand, DIN 267-28 goes further.

Two further points come from practice. On zinc flake coatings, sealers or coatings with lubricant, the breakaway torque of a micro-encapsulated locking can be below the values of DIN 267-27. Reyher therefore recommends tests under operating conditions before series production starts. And adhesive locking is limited in temperature: depending on the product, the upper limit is between 110 and 200 °C.

Which types of screw locking do not work

Spring lock washers, toothed lock washers, serrated lock washers and some other elements have been shown not to lock, and their standards have been withdrawn. Nevertheless, they are still listed in many bills of materials.

Under static load, spring lock washers to DIN 127 and DIN 128 and spring washers to DIN 137 are considered ineffective. A spring lock washer is already fully compressed at 5 percent of the nominal preload of a screw of property class 8.8. From then on it only acts like a plain washer.

Under dynamic load, serrated lock washers to DIN 6798 and toothed lock washers to DIN 6797 are considered ineffective, as are tab washers to DIN 93, DIN 432 and DIN 463, locking cups to DIN 526 and pal nuts to DIN 7967. Locking with a second nut does not secure the joint here either.

If you find one of these items on an existing drawing, it is best not to simply reorder the element. The joint should be reassessed.

Liquid during assembly or coated at the factory

Liquid adhesive applied during assembly is suitable for small quantities, and coating before assembly for large quantities. That is how Reyher classifies it.

Anaerobic liquid adhesives are only applied to the thread during assembly. They cure in the absence of air and in contact with metal and, according to Reyher, are suitable for small quantities and universal use.

Micro-encapsulated coatings, by contrast, are applied beforehand in a separate coating process. The part arrives at the line already locked, and one work step is eliminated in assembly.

For series parts, one question therefore comes before the choice of adhesive: at which point in the chain is the locking applied to the part?

How NORM+DREH handles this
With us, the thread locking comes with the fastener that you order anyway: clamping to DIN 267 Part 28, micro-encapsulated adhesive to DIN 267 Part 27, as Tuflok with a nylon layer on the thread or as NormTight filament locking. Which process is suitable depends on the thread, surface and operating temperature of your joint. Please send us your drawing, and we will check the suitable process. More on this on the page Factory-applied thread locking.

Frequently asked questions about screw locking

Which screw locking is the best?

That depends on the load. Against self-loosening under dynamic transverse load, positive, wedge-type and adhesive anti-loosening locking generally maintains the preload above 80 percent. Anti-loss locking only prevents the joint from coming apart.

How does micro-encapsulated screw locking work?

Microcapsules containing adhesive and hardener sit on the thread and break open when the screw is screwed in. The substances mix and generally cure within 24 hours. DIN 267-27 specifies the requirements for steel screws from M3 to M39.

Are spring lock washers still permitted as screw locking?

Spring lock washers to DIN 127 and DIN 128 are considered ineffective, and their standards have been withdrawn. Even at 5 percent of the nominal preload of an 8.8 screw, they are fully compressed and only act like a plain washer.

Which screw locking is heat-resistant?

Depending on the product, adhesive locking withstands up to 110 or up to 200 °C. For micro-encapsulated coatings to DIN 267-27, the limit is plus 100 °C, or 150 °C depending on the application specification; for clamping coatings to DIN 267-28, it is plus 120 °C, or 150 or 200 °C depending on the application specification. Above that, Reyher recommends metallic locking elements with positive or frictional locking.

What is an alternative to liquid screw locking?

For series production, a factory-applied coating, clamping to DIN 267-28 or micro-encapsulated to DIN 267-27. The screw arrives already locked, and manual application during assembly is no longer necessary.