Grower Twin-Lock® washers


Grower Twin-Lock® wedge-lock safety washers, differently from all other Growermetal’s type of washers, use tension rather than friction to secure the bolted-joint connection.
Grower Twin-Lock® high quality safety washers are the best technical solution to secure critical bolted connections in presence of severe vibrations and dynamic loads and can be reusable many times without loss in performance.
Grower Twin-Lock® are designed for use with bolt/nut assemblies involving fasteners of property class up to 10.9.

Products list

  • Grower Twin-Lock®
  • Grower Twin-Lock® - Large series

Dimensional charts

Technical charts

Grower Twin-Lock®

Product working principle

Grower Twin-Lock®
security system of Growermetal
to ensure the integrity of fastener thread systems works by using tension rather than friction, which has been the basis for most traditional fastening methods

This ensures the securing of threaded systems. Grower Twin-Lock® security system consists of two identical flat washers which have a set of cams on one side and a radial knurling on the other side.
The angle of inclination a of the washer cam is bigger than the pitch ß of the screw thread. When the fastener is tightened, the knurled surfaces grip both the bearing surface of the fastener and the material into which the screw is being fastened. The larger angle of the cam a, compared to the smaller angle of the screw thread ß, will not allow the screw to loosen because of the tension caused by the cam lifting.


The Twin-Lock® washers of Growermetal ensure the ultimate fastening performance for joints under extreme vibrations or dynamic loads. The exceptional securing performances of Twin-Lock® washers are guaranteed by the following technical features:

  • The unique cam angle a of the washer is larger than the pitch angle ß of the screw thread;
  • The coefficient of friction of the outside knurled surface of the washer is much higher than the coefficient of friction of the cam surface;
  • The hardness of Twin-Lock® washers is higher than the strength of all classes of bolt/nut (8.8, 10.9 and 12.9);
  • This unique cam system uses tension to create high force in a fastened joint that is subjected to vibrations.

The independent German Institute Materialprüfungsamt Nordrhein-Westfalen (MPA NRW) carried out a vibration test with the Twin-Lock® washers according to the Standard DIN 65151 (Junker Test) and certified that it is in conformity with the requirements of the Standard DIN 25201:2010 Part 4, Enclosure B (certificate n. 11 0042 11 11-01).

Grower Twin-Lock®

The test showed that the Twin-Lock® washers safely lock screws/bolt connections: the clamp force stays almost constant after 2000 cycles and just a minimal amount of tension dissipates at the beginning of the test due to the normal settlement of the fastened joint.

To develop the optimal results of the Twin-Lock® washers our R&D Department used the Junker Test Machine, in accordance with DIN 65151 Standard, to verify the performance of our washers in the presence of vibrations.
After exhaustive testing with the Junker Test Machine, Growermetal succeeded in engineering a top performing product in the presence of vibration and dynamic load. The following diagram shows the optimal security performances of Twin-Lock® washers in the presence of vibrations.

The blue diagram clarifies that is necessary to increase the clamping force in order to untighten the bolt after 2000 vibration cycles (click effect).


Thanks to its own know-how and the lab tests carried out, Growermetal can ensure the following main advantages of its Grower Twin-Lock® security system:

  • Best locking performance in the presence of vibrations and dynamic loads;
  • The system works independently from the type of lubrication used and guarantees a secure locking in dry as well as in lubricated conditions. However, Growermetal recommends the use of a high quality lubricant in order to maximize the performance of this fastening system;
  • Reusable without loss of performance;
  • Locking of fixing elements with high as well as low pre-load;
  • Can be used with any kind of bolt/nut of any class of resistance (up to 12.9);
  • No retightening required;
  • No risk of hydrogen embrittlement;
  • Assembly-friendly system as the pieces are delivered pre-glued (cams face against cams face).


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