The following methods are used to secure bolts and nuts:
In bolt-and-nut connections, nuts tend to loosen, especially if the working environment is subject to vibration. This is a situation that can lead to hazards. Various measures can be taken to lock the nut and prevent it from loosening. These measures include using a spring washer, using a lock nut, using a tab washer, using a castellated nut and cotter pin, and securing with a set screw.
Spring Washer
Spring washers are inexpensive, simple elements that create constant pressure beneath the nut. This provides partial locking.
Tab Washer
These are washers placed beneath nuts on machines subject to impact and vibration to prevent the nuts from coming undone. They come in various types: internal-tab, external-tab, single-tab, and double-tab.
Castellated Nut and Cotter Pin
This system, applied using a specially profiled nut called a castellated nut together with a cotter pin, provides positive locking.
Vibration-Induced Loosening
The most common cause of bolted connections loosening is the reduction of friction force under continuous vibration.
Tightening Torque
Bolts should be tightened with a torque wrench to the value specified by the manufacturer (usually in Nm).
Using Loctite
Chemical thread lockers (e.g., Loctite) cure between the threads, providing additional protection alongside mechanical locking methods.
Lock Nut
Using two nuts stacked on top of each other in threaded connections is called the lock nut (jam nut) technique. One of the nuts (the top one) acts as a brake against the possibility of the other loosening. This technique is used in many places to ensure the safety of working conditions. It is used especially for threaded connections that are high-strength or operate under high loads.
This technique is particularly common in construction, industrial machinery, or the automotive industry. For example, the connections between the girders of a bridge can be made with this type of threaded connection. This ensures the bridge operates safely.
Bolt Security with a Set Screw (Horizontal)
This is a locking method performed using a headless bolt known as a threaded pin or set screw. The images below show its horizontal use.
Bolt Security with a Set Screw (Vertical)
This is a locking method performed using a headless bolt known as a threaded pin or set screw. The images below show its vertical use.
Related Questions
The washer creates constant pressure (tension) between the nut and the part. This constant pressure makes it more difficult for the nut to easily turn and loosen during vibration.
The cotter pin is passed through the holes on the castellated nut and secured to the bolt; this completely prevents the nut from physically rotating. While other methods make loosening more difficult through friction, this method mechanically locks the nut.
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