Jam Nuts vs. Hex Nuts: What Is the Difference?

You may look at a jam nut beside a hex nut and wonder: what exactly is the difference? Both share a similar shape and are available in similar materials. However, there are several notable differences in their use and design. In this blog, we will clear up the confusion surrounding jam and hex nuts, including where they might best be used, and give added information about the types of nuts available.

As the name implies, hex nuts are hexagonal fasteners with interior threading that are used in conjunction with a bolt. To install, they must be twisted on to a bolt either by hand or by a wrench or similar tool. Jam nuts are very similar in their shape with six sides of equal length. However, they are designed specifically to press or “jam” against another nut. This is to help safeguard the nut and its accompanying bolt from being jolted or loosened by vibration.

A major source of confusion may be that a jam nut is actually a specific type of hex nut. Whereas hex nuts include any hexagonally shaped nut, jam nuts are jammed into another nut, thereby adding friction and keeping it secure. In keeping with this functionality, jam nuts are thinner than standard nuts so they can be placed below a standard nut on a bolt. By having two nuts pushed against each other, as opposed to one, it is less likely for the two to loosen or detach.

Overall the use of the hexagonal shape is common in nut designs because it allows for easy fastening. The six sides make it so that you only need to turn a nut 60 degrees for it to move, as opposed to the 90 degrees it takes for a square nut to make the same movement. Some other common types of hex nuts include nylon insert lock nuts, cap nuts, acorn nuts, flange nuts, coupling nuts, and castle nuts. Nylon insert lock nuts have an added fiber insert which generates more friction, keeping the nut extra secure. Cap and acorn nuts have a domed top for appearance or to avoid snagging. Flange nuts have a built-in washer to spread their weight and avoid damaging a softer surface such as wood. Coupling nuts are long nuts used to connect pieces of threaded rod and finally, castle nuts have a drilled top for use in conjunction with a cotter pin.

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