Hydraulic Tensioning Terminology

Hydraulics Technology can provide you with all the information and products you need for your specific hydraulic bolt tensioning needs. Please view our glossary below and contact us for more information.

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A metal formed by fusing two or more metals

American National Standards Institute. A non governmental organization that creates and publishes standards for use in the United States.

American Petroleum Institute – a trade association for the oil and gas industry representing about 400 corporations.

Axial Force
A pull (tension) or push (compression) that tends to elongate or shorten a member.


Bearing Stress
The surface pressure acting on a joint face directly as a result of the force applied by a fastener.

A threaded fastener with a head – used with a nut or an internal thread.

Bolt Heater
Tool used to tighten studs and bolts by heating them.

Bolt Load
Force which an externally threaded fastener exerts on the joint it is holding together.

The process of loosening the Nut from the Stud or Bolt.

Component that supports the Tensioner Load Cell and straddles the Nut. Typically has a “window” that allows access to turn the Nut during the tightening or loosening process.


Act of comparing an instrument’s measuring accuracy to a known standard.

Clamping Force
The compressive force that a fastener exerts on the joint.

Coefficient of Friction
A dimensionless number which represents the resistance to sliding between two surfaces in contact.


A component (for example, a Bolt or a Stud) that mechanically joins two or more objects together.

Finite Element Analysis (FEA)
A mathematical system for analyzing physical behavior (for example stress, and strain) of components under various loading conditions.

A projecting lip or surface on an object for strengthening it or attaching it to another object.


A wearing away of seizure of two contact surfaces caused by friction.

Component used to create a leak free seal between two surfaces.


Flexible tube to contain pressure and to carry fluids from one point to another.

Hydraulic Oil
Liquid used to generate mechanical force in a hydraulic system.

Hydraulic Tensioner
Hydraulic tool used to tighten a stud by stretching. After the Stud has been stretched, the Nut is rundown to the joint. The load on the Stud is then removed, resulting in the clamping force being transferred to the bolted joint.


An international standard setting body (International Organization for Standardization) that creates and promotes proprietary industrial and commercial standards.

ISO 9000
Family of standards to ensure quality in process and products in any organization. Administered by accrediation and certification bodies.


Load Cell
The Hydraulic Cylinder portion of the Hydraulic Nut or Stud Tensioner.


An internally threaded component used with a Stud or Bolt for clamping applications.

Nut Rotating Socket
Nut Rotating component with an internal hex that fits inside of the Bridge and snugly around the Nut. A circular rod, or “tommy bar”, is inserted into one of the holes drilled in the socket to tighten or loosen the Nut.


Power Unit
Hydraulic Pump used to pressurize the hydraulic fluid. Can be hand, air or electrically operated.

Power Load
The force a fastener can withstand without permanent deformation.

Puller (Puller Bar)
Internally threaded member that transfers force from the Load Cell to the Stud.


Quality Assurance
Planned and systematic processes that provide confidence in a product’s suitability for its intended purpose.

Quick Disconnect
Hydraulic fittings used to quickly connect or disconnect components.


The loss of fastener clamping force that occurs without nut rotation.

Residual Stress
Stress that remains in the fastener after the Stud Tensioner has been removed.


Thin metal parts used as spacers to position or align components.

Stress Area
The effective cross sectional area of a thread.

Distance a Tensioner Load Cell can move before requiring recompression.

A threaded fastener used with two nuts or one nut and an internal thread.

Stud Relaxation
The factor taken into account to compensate for the loss in clamping force due to stud relaxation.


The Process of obtaining a clamping force on a bolted joint by axially loading the Stud. The Stud is pulled to a predefined load and held there while the nut is run down. Tension on the stud is released and the load is transferred to the bolted joint.

Twisting force tending to rotate an object about an axis.

Torque Wrench
A tool used to set the torque on a fastener.


Working Pressure
Maximum rated hydraulic pressure for the equipment.


Yield Strength
Maximum Stress beyond which the material undergoes plastic deformation.

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