How to choose the best product for the various applications?

FPT shows the main utilisations

Tensionatore o superbolt super dado

There are two technical solutions that allow you to perform tensioning and clamping operations in different ways: the hydraulic tensioner and the mechanical tensioner.

The two products have different technical characteristics: the target is to know strengths and weaknesses of both in order to be able to correctly choose the most suitable solution for the specific application.


If it is necessary to carry out tensioning operations in the Industrial, Oil & Gas, Energy and Metallurgical sectors, different technologies can be used.

FPT – Fluid Power Technology wants to analyse the technical characteristics of hydraulic tensioners and mechanical tensioner or super-nut, highlighting the information necessary to make the right choice for the specific application.

The peculiarities of hydraulic tensioners and mechanical tensioners are listed in the following table:









Hydraulic acting

High leverage effect. With the minimum effort for the operator, very high forces are obtained

Hydraulic pump and flexible hoses are necessary

Mechanical acting

Construction simplicity. Requires only a torque wrench.

Greater effort for the operator. Slow procedure due to the amount of screws to be tightened

Modular configuration

With its conversion kits it can be used on a wide range of threads

Encumbrance of the superior tool

Single-threaded architecture

Extremely compact dimensions similar to a conventional hexagonal nut

Poor versatility. Each nut is designed for a certain thread

Pure traction tightening

The studs are tensioned by pure traction. The operations is very precise and repeatable.

The required forces imply high pressures. 1500 bar typically


L’utilizzo è molto semplice e non richiede attrezzature particolari

Tightening is by torsion: it is conditioned by the variability of the screw-nut screw friction

Contextuality of the operation

Using appropriate hydraulic connections it is possible to perform a simultaneous tensioning on several studs

The number of tensioners must be equal to the number of studs that must be tensioned contextually

Individuality of the operation

No plus. Moreover, being a nut, the necessary quantity is equal to the number of studs to be tensioned

It is necessary to provide an accurate tightening sequence to uniform the load


The tensioner is used only for tensioning operations and then it is removed

Tightening many bolts requires the same number of assembly and disassembly

Integration with machinery

It is designed as a nut becoming an integral part of the machine. The nut is mounted only once

The necessary quantity is often high and it is equal to the number of studs to be tightened

Heat sources

Appropriate design characteristics allow the realisation of tensioners for high temperature

Maximum temperatures are in function of the seals. 180/200°C is max. value

Heat sources

Heat resistance is high because they are only steel-made. Alloy solutions allow to reach more than 500°C

Long time of exposure at high temperature can cause corrosion

For more information, contact the FPT technical department