What is a Check Nut?

A check nut is used to ensure that a nut, once installed, will stay in place. Check nuts, also called lock nuts, are usually thin and used in instances where there is a high probability of the first nut shaking or vibrating loose. These nuts are designed and used to prevent the first nut from becoming loose and potentially causing damage or injury when using a device. Lock nuts, or check nuts, were designed to replace lock washers, which did not work as well at preventing loosening over time from movement and vibration.

The modern day lock nut is typically made to look like the normal castle nut. There is, however, a nylon inset on the inside portion of the check nut. The nylon inset is the key component of the nut.

When properly installed, the nylon inset on the check nut grips the threads. This allows the nut to take a firmer hold on the bolt or stud it is being applied to. This feature ensures the nut will stay firmly in place and not shake loose due to movement and vibration.

Check nuts will only work as they are supposed to when they are properly installed. To install a check nut properly, it is necessary to have the stud or bolt the nut is being applied to and one or two correct sized wrenches. Next, the user must take the nut in hand.

To install, the user must slide the check nut over the shaft of the bolt or stud and turn it in a clockwise direction until the nylon inset on the inside of the nut catches the first thread. It will be clear when it has done this because the user will feel some resistance and will no longer be able to turn it by hand.

Once the user feel this resistance, he must grab the correct size wrench and turn the nut the rest of the way down the shaft of the stud or bolt with the wrench. This will ensure a tight fit. It must be turned until the lock nut sits just against the other nut. If needed, the second wrench can be used to hold the other end of the shaft of the stud or bolt. A tight fit against the shaft and against the first nut will ensure that the lock nut will perform its key function of keeping the other nut from loosening over time due to movement and vibration.