How do Superbolt tensioners work?

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.

superbolt tensioner installation diagram

Superbolt tensioners from the Nord-Lock Group consist of three components:

  • A hardened washer (3) protects your equipment and provides a hardened, flat surface for the jackbolts to “push” against.
  • The nut body (2) spins on your existing bolt or stud and seats against the washer hand tight (Superbolt nut bodies are typically round).
  • The jackbolts (1) thread through the nut body and are used to tighten the joint in pure tension, using ordinary hand tools.


Superbolt tensioners working on a bolted joint:

  • By tightening the jackbolts (1), 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.
  • The loads are transferred through the nut body (2) which is positioned on the main thread by hand.
  • A hardened washer (3) is used to transfer the force while protecting the flange face.
  • 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 (4).
  • The thrust (axial) force from the jackbolt creates an equally strong reaction force in the main bolt (5).