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  1. Böllhoff Switzerland
  2. Products
  3. Special fasteners
  4. Twin-Lock

Screw locking

Twin-Lock

Form fit over friction: Twin-Lock delivers a convincing performance with innovative locking technology.

Benefits Product types
Product image of a Twin-Lock lock washer.

For optimum locking action

Defies strong vibrations: Twin-Lock harnesses the pre-tensioning force of the connection

Twin-Lock meets all your locking requirements. The special interlocking design of the Twin-Lock washer pairs makes them superior to conventional screw locks. The anti-loosening mechanism is based on pre-tensioning force instead of friction and achieves peak performance under difficult conditions.

Plus factors

Advantages of Twin-Lock

  • Optimum locking action

    The Twin-Lock locking system works even under strong dynamic stress and vibrations.

  • Application-oriented

    Whether dry or lubricated surfaces – Twin-Lock achieves the desired locking effect.

  • Easy to assemble

    The pre-glued twin washers are easy to handle. They prevent errors during initial assembly.

  • Environmentally friendly and corrosion resistant

    Thanks to the high-quality coating, Twin-Lock is particularly corrosion-resistant and completely Cr6-free.

  • Reusable

    You can unscrew the screw lock easily and reuse it without any loss of function.

  • High durability

    Twin-Lock has proven effective with screws and nuts of all strength classes – up to and including 12.9.

Twin-Lock – the perfect locking solution

  • Pair of Twin-Lock wedge-locking washers

  • Twin-Lock product family

Method and principle

Innovative screw lock prevents screws from working loose

Twin-Lock consists of two identical wedge-locking washers with radial teeth on one side and a spline on the other. The washers are glued together in twos, so that the wedge surfaces lie on top of each other on the inside.

As soon as you tighten the screw or nut, the radial ribs of the twin washers are pressed tightly into the mating surface and the screw head. The helix angle of the spline is greater than the helix angle of the screw thread. This means that the pre-tensioning force increases when the screw connection is loosened. In addition, the coefficient of friction of the radial toothing is significantly higher than that of the spline. The combination of the paired washers creates a strong unscrew lock, even when used under difficult conditions.
 

Graphic of the angle of the wedge surfaces and thread pitch angle.
The Twin-Lock method The angle of inclination α is greater than the thread pitch β

Installation and use

Versatile unscrew lock

The Twin-Lock mechanical screw lock delivers a convincing performance in many applications – whether for threaded holes (1), counterbored holes (2), through holes (3) or studs (4).

Two pairs of locking washers should be used for through holes. We recommend that you use Twin-Lock washers with enlarged outer diameters for slotted holes and soft mating materials. Do not use the wedge-locking washers on unsecured backing washers!

Four examples of Twin-Lock lock washers in use.
The Twin-Lock installation process the Twin-Lock screw lock is multifunctional

Vibration test with Twin-Lock washers

The Junker vibration test is a proven quality control method for testing screw connections. It tests and compares how secure connections are.

Twin-Lock delivers a strong performance in the rigorous vibration test. The screw lock reliably keeps the pre-tension in the connection. By contrast to screws without a locking element (red line), the pre-tensioning force for Twin-Lock is constant over the entire stress period (green line). The blue line represents the increase in force required to loosen the connection after it has undergone load changes (click effect).

Legend
Green = M8 screw with Twin‑Lock with a preload of 50 % of the yield point
Red = M8 screw without lock washer
Orange = M8 screw with conical spring washer
Yellow = M8 nut with polyamide ring
Blue = Change in preload force while the screw is loosening (click effect)

Junker diagram shows different locking effects.
The Junker vibration test Twin-Lock maintains the pre-tensioning force in the rigorous vibration test

Find the right solution for your application

Twin-Lock product types

  • Twin-lock with standard diameter

    The Twin-Lock standard design is suitable for a wide range of applications – including countersunk bolts. The lock washers are available in a wide range of materials and coatings.

    Materials

    • Tempered carbon steel, hardness 465-550 HV10
    • Stainless steel AISI 316 in accordance with EN 10088 – 1.4404, surface hardness ≥ 550 HV0.05 after surface hardening (Kolsterising®)

     

    Surface coating for carbon steel

     

    • Delta Protekt® KL100 + VH301 GZ, Cr6-free, corrosion resistance min. 600 hours (salt spray test in accordance with ISO 9227)

  • Twin-Lock with enlarged outer diameter

    The Twin-Lock wedge washers with enlarged outer diameters are ideal for soft materials and slotted holes. This design is available in a variety of materials and coatings.

    Materials

     

    • Tempered carbon steel, hardness 465-550 HV10
    • Stainless steel AISI 316 in accordance with EN 10088 – 1.4404, surface hardness ≥ 550 HV0.05 after surface hardening (Kolsterising®)

     

    Surface coating for carbon steel

     

    • Delta Protekt® KL100 + VH301 GZ, Cr6-free, corrosion resistance min. 600 hours (salt spray test in accordance with ISO 9227)

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