Sealing technology


High-strength screwing and maximum sealing. With SEAL LOCK® one-piece sealing nuts.


For a perfect seal

SEAL LOCK® sealing nuts provide a reliable seal against gas or liquids, even under high pressure.

Easy to install, doubly reliable. SEAL LOCK® seals simultaneously inside the thread and below the head. The one-piece sealing nuts are easy to fit.

This product is made by Böllhoff

Method / principle

SEAL LOCK® sealing nuts are one-piece structural elements. Sealing against leakage is possible in the thread as well in the bearing face. Moreover, SEAL LOCK® sealing nuts provide a high-strength threaded connection with no loss of preload force – even with repeat screw fastenings.


SEAL LOCK® sealing nuts are used for example in hydraulic control systems for sealing and locking adjusting screws in the return chamber of a directional control valve block. Additionally, they can be used for locking setscrews on the pressure-relief valve of internal gear pumps or for sealing and locking on the control lever shaft of the flow regulator for aircraft refuelling systems.

Product benefits
  • One-piece element
  • Effective seal
  • High preload force
  • Up to 5 repeat fastenings
  • Dimensions M 6 – M 16

Product benefits

There are many good reasons for using our products.

Strength and options.
Point by point.

Effective seal

Double sealing action. The sealing nuts seal simultaneously inside the thread and below the head against liquids and gas.


Resistant to heat and cold. SEAL LOCK® sealing nuts are temperature-resistant from ‑40°C to 110°C.

High preload force

The metal coating prevents a loss of preload force when the sealing ring is installed.

Wide choice of dimensions

Our standard range includes coarse and fine threads from M 6 to M 20. Other dimensions and special solutions are possible on request.

Detailed description



The SEAL LOCK® sealing nuts offer many advantages compared to multi-piece solutions consisting of cap nut, locknut and two sealing discs. They save assembly time and produce an optimal screwed connection without loss of preload force – and with minimal space requirements.

SEAL LOCK® sealing nuts

Product variants

Every project deserves a tailor-made solution.

Learn more about the product types and find the right variant for your particular application.

SEAL LOCK® standard

The reliable solution for sealing bolt / nut connections.



Find out more: related downloads.

If you would like to know more, simply download the relevant brochures.

Title Language Version File Download
Sealing nuts for high-strength screw joints
English 01/2018 356 kB / PDF
English 01/2018 356 kb / PDF

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