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The simple way to securing large bolted joints

Tensioning of large bolted joints usually requires the use of electric, hydraulic or pneumatic tools, adding extra costs and delay. The unique design of the HEICOTEC ® tension nut eliminates the requirement for such specialist tools as the user only requires a hand held torque wrench to achieve the required tension, resulting in savings in both time and money.

The HEICO-TEC® design consists of the nut body that is screwed onto the main thread just like a conventional nut – but it is not tightened. Several thrust bolts with associated pressure pins are arranged around the main thread inside the nut body. The smaller size of these thrust bolts means a conventional torque wrench is all that is needed to achieve the required pretension force. As the thrust bolts are tightened one by one they push the pressure pins against the clamped parts while simultaneously elongating the bolt. The pre-tension force created in this way is purely axial and therefore free from harmful torsion or bending. An incorporated hardened disk protects the tensioned parts from high pressure loads caused by the pressure pins.

When tightening a bolt with a hydraulic cylinder the bolt is elongated and the nut is then tightened free of load. When the hydraulic pressure is released the bolt contracts, resulting in the proper tension in the bolt being achieved. But as the nut was not pre-tensioned while the bolt was elongated, a percentage of the elongation of the bolt is lost in joint settlement meaning only around two thirds of the bolt strength can be utilized.

As the stress on the bolt with HEICO-TEC® is purely axial, not torsional, thread friction and deformation is greatly reduced, ensuring that the full load-bearing capacity of the bolt can be utilized. Also the loss of elongation of the bolt that occurs from joint settlement as a result of using hydraulic tensioning is not present and full capacity of the joint is achieved.

As this innovative product meets all the requirements of DIN EN ISO 898-2 it can easily be used as a direct replacement for any hex nut from the same strength class whilst also offering all the advantages of a hand-tightened nut with no need for time consuming calculations and formulas to determine suitability.

The inherent mechanical flexibility of the HEICO design means the bolted joint performs as if it has a greater clamping length. This makes it highly resistant to loosening forces and, as the assembly is not damaged during tightening and loosening, is totally reusable with its greater flexibility reducing the bolted joint’s dynamic stress and increasing its service life.

With HEICO-TEC® working with large bolted joints is now more simple, fast and reliable.

For further information visit: or contact HEICO on: 01268 745421 or

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