How Ribbed Fasteners Prevent Rotational Loosening

3 Things You Never Knew About Stainless Steel Fasteners

In many applications, one loose fastener can impact the structural integrity of the equipment it’s used in, causing delays or safety hazards. In many instances, vibrations and shock can cause a bolted joint to undergo rotational self-loosening. In these situations, vibrations can cause a fastener to rotate slightly within the joint, causing it to become loosen.

To understand the effects of vibration on a bolted joint, an engineer by the name of Gerhard Junker devised what is known as the Junker vibration test in the late 1960s. This test, which has become the standard for analyzing fasteners for self-loosening, measures how much vibration is needed for the fastener to start rotating. This is because the vibration often causes a nut or a bolt head to slide in relationship to the joint. As a result, the fasteners become loose and lose their preload within the joint.

To prevent this type of loosening, washers with ribbed, serrated surfaces have been designed to lock fasteners into place. There are many varieties on the market, including:

  • Ribbed Lock Washers
  • Rip-Lock Washer One Sided Ridges
  • Ripp Lock Washer
  • NordLock Washer
  • Durlok Wedge-Lock Washer
  • TENSILOK Screw
  • Durlok Flange Screw

While each fastener may be better suited for specific applications, they all have ribbed surfaces to prevent the fastener from becoming loose. They are also all typically made of hardened spring steel and can either be mechanically plated or zinc-flake coated.

Some fasteners are serrated on both sides, while others may have this feature only on one side. Some washers, like NordLock washers, are used in pairs to increase washer thickness and create the locking effect. With serrated bolts, the serrated edge of the bolt’s head penetrates into the clamped metal, reducing its ability to become loose when exposed to vibrations. Some of these fasteners limit reusability because of how deep the serrated edge cuts into the clamped metal.

With many variations of these fasteners available, choosing the right one for your needs can be a challenge. Contact the fastener experts at One Monroe EFI. We’ll help you select the right fasteners depending on the application and conditions they will be exposed to.