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Multi-Jackbolt Pretensioner: Best bolting solutions ...

We are an experienced Swiss engineering company with a focus on globally unique bolting solutions based on the MJP principle (mechanical Multi-Jackbolt Pretensioner) for absorbing the greatest forces.

PLOKE Multi-Jackbolt Pretensioners (MJP) are the ideal solution for large screw connections (≥ M16) where a defined pre-tensioning force needs to be generated and reliably maintained – and also easily released again! They are designed according to ISO 898-2 and are used for general screw connections in all areas of industry.

With PLOKE Multi-Jackbolt Pretensioners (MJP), an extremely advantageous geometry is achieved purely mechanically:  The pretensioning force acts purely axially and no torsional loads occur during pretensioning, so that pretensioning to 90% of the yield strength can be achieved effortlessly. For the user, this means that compared to other tensioning methods, a better load distribution in thread and support as well as lower stress peaks and thus lower settlements are achieved. The bolt cross-section of the main thread can be loaded higher and the risk of failure decreases.

In addition, due to the compact design and the resulting weight reduction, new constructions can be designed with an alpha factor >1.2, which leads to an overall more compact bolted connection with a correspondingly slimmer overall design and, at the same time, more built-in safety. 

Due to the captive mounted Mammoth™ Jackbolts, PLOKE Multi-Jackbolt Pretensioners are thus ideally suited for highly dynamic applications such as turbine impellers.

The defined pretensioning force is generated by the systematic tightening of the Mammoth™ Jackbolts. Due to the special shape of these Jackbolts, on the one hand the largest possible pressing surface is achieved, and on the other hand, due to the small friction radii, only a minimum clamping torque MA is required, which can be easily achieved with simple hand tools. The final pretensioning force FV in the screw bolt (main thread) consequently corresponds to the sum of the Jackbolt forces; it is purely axial and thus torsion-free. The clamping force of the connection results from the compressive force of the Mammoth™ Jackbolts and the reaction force in the screw bolt.

... with the simplest handling

PLOKE Multi-Jackbolt Pretensioners (MJP) are basically not subject to any wear and can therefore be pretensioned, loosened and retensioned as often as required.

Since bolted connections with PLOKE Multi-Jackbolt Pretensioners (MJP) can be loosened and retensioned extremely quickly and only small forces are used, only the shortest downtimes result for the user both when replacing conventional bolted connections and during maintenance work on the plant. This in turn means great financial advantages due to the significant increase in the availability of production plants.

In addition, when bolting with PLOKE Multi-Jackbolt Pretensioners (MJP), simple and commercially available hand tools (torque wrenches) can be used. Special tools are not required and a short introduction of the operating personnel is sufficient.

Another plus is the external hexalobular head (Torx®) of the Mammoth™ Jackbolts: this is extremely wear-resistant and safe to handle, which contributes to work safety.

PLOKE Multi-Jackbolt Pretensioners (MJP) are protected by patent:

  • Internationale PCT-Patentanmeldung WO2018/065898
  • United States Patent No.: US 11,092,186 B2

Reliable bolting with controlled preload – axial and radial

We offer our services and products throughout Europe. Our customers are advised personally and competently on site by our sales engineers and distribution partners and are also supported during the installation of their bolting solution or during maintenance work. Benefit from our many years of experience as a technology leader for highly stressed large diameter screw joints.


Safe bolting solutions for all areas of industry – with over 30 years of experience

PLOKE Multi-Jackbolt Pretensioners (MJP) are used for large bolted connections in all areas of industry. Where our standard series do not provide an optimal solution, we develop customized special designs. Benefit from over 30 years of know-how – put your trust in the original: PLOKE Multi-Jackbolt Pretensioners guarantee the best bolting solutions.