Grower Twin-Lock®

Performances and advantages

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:


  1. The unique cam angle a of the washer is larger than the pitch angle ß of the screw thread;
  2. The coefficient of friction of the outside knurled surface of the washer is much higher than the coefficient of friction of the cam surface;
  3. The hardness of Twin-Lock® washers is higher than the strength of all classes of bolt/nut (8.8, 10.9 and 12.9);
  4. 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).

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:

  1. Best locking performance in the presence of vibrations and dynamic loads;
  2. 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;
  3. Reusable without loss of performance; 
  4. Locking of fixing elements with high as well as low pre-load;
  5. Can be used with any kind of bolt/nut of any class of resistance (up to 12.9);
  6. No retightening required;
  7. No risk of hydrogen embrittlement;
  8. Assembly-friendly system as the pieces are delivered pre-glued (cams face against cams face).