Multi-jackbolt tensioners (MJTs)

Bolting Made Simple

The Nord-Lock Group manufactures patented Superbolt multi-jackbolt tensioners designed to eliminate unsafe and time consuming bolting methods. MJTs replace or retrofit existing nuts and bolts, and only require hand/air tools for installation and removal of any size tensioner.

Thousands of companies have enjoyed the benefits of using our bolting products. Switching from other bolting methods (such as hydraulic torque wrenches and stud heaters) can save you money and increase worker safety. Also, MJT's offer a better bolted connection than conventional hex nuts. Discover all the benefits below!

  • 1. A hardened washer protects your equipment and provides a hardened, flat surface for the jackbolts to "push" against.

    2. The nut body spins on your existing bolt or stud and seats against the washer hand tight (Superbolt nut bodies are typically round).

    3. The Jackbolts thread through the nut body and are used to tighten the joint in pure tension, using ordinary hand tools.

What is a multi-jackbolt tensioner?

A «Superbolt» or «multi-jackbolt tensioner (MJT)» is a direct replacement for hex nuts, covered nuts, bolts, etc. They spin onto your existing bolt or stud and provide a better way to bolt up your joint. They consist of three components, shown to the left.

If you are tightening a nut greater than 1″ in diameter, you may find Superbolts useful, since the torque you need to tighten conventional nuts and bolts exponentially increases as the size increases. Our products solve this problem and only require hand/air tools to install or remove any size MJT. They eliminate the need for time consuming and unsafe bolting equipment such as sledgehammers, hydraulic wrenches and stud heaters.

Multi-jackbolt tensioners come in a variety of sizes and configurations. We have many stock items that are available for immediate shipment, and we are able to handle custom jobs quickly. If you are experiencing bolting problems such as leakage, thread galling, unsafe working conditions or are using expensive methods and find it difficult to properly bolt your joint, Nord-Lock bolting technologies are the solution for you.

MJT Brochure: Click here!

  • 1) By tightening the jackbolts, a strong thrust (axial) force is generated. This thrust force is directed against a hardened washer. Jackbolts have a small friction diameter and can therefore create a high thrust force with relatively little torque input.

    2) The loads are transferred through the nut body which is positioned on the main thread by hand.

    3) A hardened washer is used to transfer the force while protecting the flange face.

    4) The thrust (axial) force of many jackbolts and the opposite reaction force of the main bolt head create a strong clamping force on the flange.

    5) The thrust (axial) force from the jackbolt creates an equally strong reaction force in the main bolt.

How MJTs work

The Superbolt multi-jackbolt tensioner (MJT) takes the high preload requirements in large diameter bolting and breaks it down into manageable torques using the jackbolts threaded through the nut body. Superbolt tensioners remain easy to install, even on larger sizes, compared to standard hex nuts.


The advantage is obvious, but how exactly do our multi-jackbolt tensioners achieve this? As you can see in the animation below, the hardened washer is installed first. Then the nut body is threaded onto the existing stud or bolt, hand tight against the washer. The jackbolts are then tightened and thrust against the hardened washer. Accurate preload is achieved on the stud by torquing the jackbolts.

Our bolting technologies come in a variety of custom configurations, meeting the requirements of virtually every type of application. MJTs are available in both nut and bolt style, and we also can supply studs, expansion bolts, flexnuts, thrust collars and more. Visit our products page for more information.

Advantages of Superbolt tensioners

Multi-jackbolt tensioners (MJTs) offer many benefits when compared to other common bolting methods. They are fast, safe and easy to use!

  • Tremendous clamping force available.
  • Low torque requirement – only hand tools needed.
  • Safe method for installation personnel.
  • Reduces installation time over common methods.
  • Tightens stud/bolts in pure tension.
    – No thread galling.
    – No need for tight tolerance threads which can seize.
    – Studs will not seize into housing.
  • Tensioner flexibility adds elasticity to studs/bolts to create a better bolted joint.
  • Fits in restricted areas.
  • Provides even tension from stud to stud.
  • Accurate within 10% of specified bolt tension.
  • Ease of removal.

Proven in the field

Case studies:

Superbolt tensioners are used in all industries, all over the world. To learn more about how this technology has helped other companies with their bolting challenges, please use the links below:



Over the years, the product types in our multi-jackbolt tensioners range have been tested and approved by several certification institutes and authorities. We have also achieved several design approvals and type approvals for production. Below are some examples:

  • DNV (Det Norske Veritas)
GL (Germanischer Lloyd)
  • TÜV


All of our products can be delivered with additional certificates upon request. Additional certificates should be requested prior to ordering in order to assure proper compliance. For more detailed information on certificates / approvals for a specific product or production site, please contact your local Nord-Lock office.

About the acquisition

The Nord-Lock Group has acquired both Superbolt, Inc. and P&S Vorspannsysteme AG (now known as Nord-Lock AG). This exciting combination of the competence of Superbolt and Nord-Lock is unique in the bolt securing industry. We are able to serve global customers with an impressive line-up of safe and cost effective bolting solutions for critical applications.

If you are looking for contact information for either of these companies, see below:

Superbolt Inc
1000 Gregg St
Carnegie PA 15106

Tel: +1 412 279 1149
Fax: +1 412 279 1185

Nord-Lock AG
Rietwiesstrasse 2
8735 St. Gallenkappel

Tel: +41 (0)55 284 64 64
Fax: +41 (0)55 284 64 69

For information about Nord-Lock representation in your area, please refer to our contact page.


  • Nut-style tensioners

    Achieve high & accurate preload with only hand tools! Replaces existing nuts.

  • Bolt-style tensioners

    Achieve high & accurate preload with only hand tools! Replaces the existing bolt or stud. Requires less space than nut and stud configuration.

  • Flexnuts

    For through hole applications. Ensure an equal load distribution & increase fatigue life of the bolt/stud.

  • Expansion Bolts

    Replaces traditional interference or force fit bolts. Utilizes multi-jackbolt technology.

  • Pre-designed solutions & specials

    Unique MJT designs for specific application challenges.