Lock Nut Types: Nylon Insert Lock Nuts, Jam Nuts, and Bearing Lock Nuts

Lock nuts with nylon inserts (self-locking nut, locking nut), are a prevailing torque locking nut that resists loosening caused by vibration and normal use. 

Unlike free spinning nuts, lock nuts feature a deforming elastic or metal material that fortifies the secured threaded position to resist torque and shock. Lock nuts with nylon inserts are a popular solution for many applications; however, they are limited to applications exposed to temperatures under 250°. 

Prevailing torque lock nuts are installed with the nylon locking end of the nut positioned at the bottom of the mating threads. When installing, the nut should thread on freely until the mating threads of the host component engage the nylon insert.  

For safety reasons, it is not recommended to reuse a nylon lock nut because it loses prevailing torque with each use. Once a nylon lock nut is installed, the nylon insert is deformed; if you were to remove the nut and reinstall it, its locking strength would be lost.  

Jam nuts, or half nuts, are a low-profile hex nut with a profile half the height of a standard hex nut. Jam nuts are used as a locknut to prevent vibration from loosening a bolted joint. Before nuts were developed with self-locking capabilities, two jam nuts would be tightened against each other so that nuts wouldn’t loosen over time. 

Jam nuts use opposing friction against either another jam nut or a standard hex nut to lock into position on a threaded shaft or rod. There are conflicting view points on which nut should be installed first, however the most common use case involves the jam nut being tightened down first. The jam nut is followed by the second nut which is tightened or “jammed” against the jam nut.

It is difficult to get both nuts properly torqued in this configuration, which makes it undesirable for critical applications where the assembly carries a tension load.

Bearing lock nuts, sometimes called shaft locknuts or bearing retaining nuts, secure bearings onto a shaft and prevent components from loosening due to vibration and rotation. Bearing locknuts possess a different appearance from traditional hex lock nuts. Bearing locknuts are typically rounded on the outside with keyed slots. This design requires a special tool called a spanner wrench or socket to be installed or removed. Bearing locknuts are used in a wide variety of applications including the automotive and agriculture industries.