8 Effective Bolt Locking Methods

There are three commonly used bolt locking methods, which include friction locking, mechanical locking and permanent locking. Permanent locking that is called non removable locking includes welding, riveting, bonding, etc, which usually destroys threaded fasteners during disassembly and can’t be reused. Common friction locking methods include washer, self-locking nut, double nut, etc. Here we introduce 8 effective bolt anti-loose methods.


1. Double nut

When the double nut is locked, two friction surfaces are generated. The first friction surface is between the nut and the fastener, and the second friction surface is between the nut and the nut. During installation, the preload of the first friction surface is 80% of the second friction surface. Under the impact and vibration loads, the friction force on the first friction surface will decrease and disappear, but at the same time, the first nut will be compressed to further increase the friction force on the second friction surface. The nut loosening must overcome the first friction and the second friction, because the second friction will increase while the first friction decreases. In this way, the anti loosening effect will be better.

2. Self locking nut

Self-locking nuts are generally self-locking by friction. It is divided into high-strength self-locking nuts for road construction machinery, mining machinery, vibration machinery and equipment, and Nylock nuts for aerospace, tank, mining machinery, etc.


3. Wedge Nord lock washer

Radial serrations on outer surface of the wedge lock washer engage with the surface of the workpiece it contacts. When the locking system is subjected to dynamic load, displacement can only occur on the inner surface of the washer.

The expandable distance along the thickness direction of the wedge lock washer is greater than the longitudinal displacement of the bolt along the thread. It is completely different from other bolt locking methods. It uses clamping force instead of friction to tighten bolts.

4. Cotter pin and slotted nut

After the nut is tightened, insert the cotter pin into the nut slot and the bolt tail hole and pull open the split pin tail to prevent the relative rotation of the nut and bolt. Slotted nuts are used together with threaded rod bolts with holes and cotter pins to prevent the relative rotation between bolts and nuts.

5. Lock washer

After the nut is tightened, bend and stick the lock washer to the side of the nut and the connector to lock the nut. If two bolts need to be tightened by double interlocking, double lock washers can be used.


6. Spring washer

The anti loose principle of spring washer is that after the spring washer is pressed, the spring washer will produce a continuous elastic force, which will keep a friction force between the nut and the threaded connection of the bolt, generating a torque to prevent the nut from loosening. At the same time, the sharp corner at the opening of the spring washer is embedded into the surface of the bolt and the connected piece respectively, which prevent the bolt from rotating relative to the connected piece.


7. Hot melt fastening technology

The hot melt fastening technology does not require pre opening and connection can be realized by direct tapping under closed profiles, which is widely used in the automotive industry.

This hot melt fastening technology is a cold forming process that conducts the high-speed rotation of the motor through the central tightening shaft of the equipment to the plastic deformation caused by the friction heat of the connecting plates, then self tapping and screw connection.

8. Pre-tightening

In general, high-strength bolt connection does not require additional anti loosening measures, because high-strength bolts generally require a relatively large pre-tightening force that will generate a strong pressure between the nut and the connected part, which will generate friction torque to prevent the nut from rotating, so the nut will not loosen.

Fastener locking is important. Hope the 8 methods can help you to get best locking bolt.

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