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Success stories

Kupplungswerk Dresden

Tampering protection – for sure

Train passing through a station.

The PARRYPLUG® tampering protection for screws

For KWD, it provides a quick and safe solution to prevent unauthorized loosening of bolted connections.

Initial Situation

Unintentional manipulation by service technicians

Gear coupling transmits high torques such as those required in the railway sector. However, with rail traffic there is always strong vibration to be taken into account. This means that the fasteners that are used here, such as the ones that are fixed to the flange cover (M6 x 12 here), also have to be secured with a microencapsulated adhesive so that they do not loosen by themselves in operation.

In railroad companies it can happen that replacement products like such couplings are stored for years before they get installed. This has led to problems in the past as the screws have loosened and even been lost in operation. This has resulted in complaints about the couplings for KWD. Following escalation meetings, it transpired that service installers of the end customer had opened the lids on some of the couplings so that the screw lock had become ineffective and the screws may loosen in operation.

Gear coupling in the railroad industry
The gear coupling loosened during operation.



PARRYPLUG® prevents interference with tools in the internal drive of the screw due to specially designed axial ribs, which ensure a defined and secure tight fit. The high-performance plastic used with its wide application range from -50°C to +200°C, combined with high manufacturing precision, ensure that even the finest tolerances of hexagon drives can be taken into account. PARRYPLUG® is now used in the flange bolting to exclude such tampering. Should the plug be removed without authority, the warranty claim is cancelled, in the same way as with sealing, but much simpler to install. Unauthorized removal causes damage to the plug so that it cannot be put back on afterwards. PARRYPLUG® has convinced KWD – and is now used in all applications where unauthorised opening of screws must be prevented or at least made apparent.

PARRYPLUG® close-up with axial ribs emphasized
PARRYPLUG®'s axial ribs generate a secure press-fit


Customer benefits

The unauthorized loosening of bolts on machines and systems poses a high potential risk. It is therefore often necessary to effectively prevent unintentional tampering. While conventional solutions irrevocably destroy the screw drive, PARRYPLUG® offers a completely new and innovative solution.

  • Reliable and convenient installation
  • An optimally tight fit provides maximum protection against tampering
  • Clean and visually appealing solution
  • Can be removed with the appropriate tool
  • Wide temperature range (-50 °C to +200 °C)
The PARRYPLUG® three-step installation process explained.
PARRY PLUG® convenient installation ensured through handling aid