10 Classic Bolt Anti- loosening Designs for Your Collection!

Jack Lie CNC machining expert

Specialize in CNC Milling, CNC Turning, 3D Printing, Urethane Casting, and Sheet Metal Fabrication Services.

In mechanical equipment, the loose bolt connection could cause the bolt to fall off and major safety hazards, or the loose bolt and the reduced pre-tightening force could cause bolt fatigue and shorten the life of the bolt. Therefore, appropriate anti-loose measures should be selected in the design to ensure safety in actual use.

The common anti-loosening measures in design are as follows:

1.Double nuts

Anti-loosening with double nuts is also called anti-loosening with counter nuts. When two counter nuts are tightened, there is always interaction pressure between the two counter nuts, and any one nut needs to overcome the bolt thread friction to be rotated. Even if the external load changes, the pressure between the counter nuts always exists, so it can play the relaxing function.

2.Self-locking nuts

Self-locking nuts generally rely on friction for anti-loosening. The principle is to press embossing machine into the preset holes of the sheet metal. Generally, the hole diameter of the square preset holes is slightly smaller than that of the rivet nut. A nut is used to connect with the locking mechanism. When the nut is tightened, the locking mechanism locks the bolt thread.

3.Thread locking glue

Thread locking glue is an adhesive composed of (meth)acrylate, initiator, accelerator, stabilizer (polymerization inhibitor), dye and filler in a certain proportion.

4.Split pin

After tightening the nut, insert the cotter pin into the nut groove and the bolt tail hole, and open the tail of the cotter pin to prevent the nut and bolt from rotating relative to each other.

5.Slotted nuts

Slotted nuts are used in conjunction with screw bolts with holes and split pins to prevent the bolts from rotating relative to the nut.

6.Tandem wire for anti-loosening

The tandem wire for anti-loosening is to insert the steel wire into the hole of the bolt head, and connect the bolts in series to restrain each other. This way of anti-loosening is very reliable, but it is not convenient to disassemble it.


High-strength bolt connections generally do not require additional anti-loosening measures, because they generally require a relatively large pre-tightening force, which generates a strong pressure between the nut and the connected part. This pressure generates friction torque that prevents the nut from rotating, so the nut will not loosen.

8.Stop washer

After the nut is tightened, bend the single-ear or double-ear stop washer to the side of the nut and the connecting part, respectively, to lock the nut. If two bolts need double interlocking, a double brake washer can be used to make the two nuts brake each other.

9.Spring washer

10.Double stack self-locking washer