Jam Nuts

Thin Nuts For Locking Against Each Other

Jam nuts, also known aptly as thin nuts, are low profile hex nuts about 2/3rd the thickness of a standard hex finish nut. They are commonly used as a kind of locknut but may also be found in situations where a standard nut would not fit.

A jam nut is often used when a nut needs to be locked in place without clamping against another object. The jam nut essentially acts as the "other object," as the two nuts are tightened against each other. They can also be used to secure an item on a fastener without applying force to that object. This is achieved by first tightening one of the nuts onto the item. Then the other nut is screwed down on top of the first nut. The inner nut is then slackened back and tightened against the outer nut.

This locking action helps to avoid compression of the part being fastened while also locking it in place but still rotate freely, such as in bearings. The idea behind a jam nut is that a thin nut exerts less overall force than a fully torqued standard nut. They're the opposite of most heavy styles for nuts.

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How to Use Hex Jam Nuts

How to Use Jam Nuts
Using Jam Nuts Transcript

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Bob: This is what they call a jam nut. Jam nuts are about half the size of a regular finish nut in height. Otherwise the circumference and everything else is the same; they use the same wrench to apply the nut and to remove the nut.

Jam nuts, just to give you an idea what these do, you use two nuts together and then you tighten them up against each other. That's why they call them jam nuts: you use them together, you tighten them up, and I'll show you. I'll do a demonstration of that also, but typically that's how they're used. They're also used in tight areas where you can't have a full-size nut.

So I'm going to demonstrate the installation of the jam nuts that I have here. I have two of them. Jam nuts are also called thin nuts. The difference is that they're about half the size of a regular nut. You can see that here.

I'm going to put the first one on and then I'm going to put the second one on. I'm going to use an adjustable wrench to grab the bottom nut. Then I'm going to use the ratchet on the top to tighten it up.

Now I'm tightening them up against each other. That's one of the reasons why they call them jam nuts. Jam nuts are also available in nylon lock nuts where you don't have to use this situation. Obviously jam nuts can be used in many different applications such as if you have a tight area like in a car application where you don't have the room to use a regular sized nut. They'll use jam nuts or a single jam nut to get on the back of an alternator for a bracket; something along those lines. They also use the nylons in that situation.

So there's many different situations that you can use this in. They also sometimes want to put a jam nut like this to wherever it's keeping in place. They want this whole mechanism to be able to turn and move because they might be a moving arm on this bolt holding it in place. They also are used with shoulder bolts. So you'll find jam nuts used with shoulder bolts a lot on mechanical equipment. However you should know that if this is being used in a vibrating machine or something along those lines, these do have a tendency to loosen apart.

So if you want them to stay use some Loctite or some other locking product to keep them in place like they are here. And that's it.

FAQs

What is a jam nut used for?

Jam nuts are low profile nuts commonly used as a type of locknut, where it is "jammed" up against another nut. With both nuts being fastened towards each other, this effectively locks the assembly in place. You may also find these nuts used in applications where a standard nut won't fit.

What is the jam nut method?

The jam nut method, sometimes known as the "double nut" method, is a friction locking method that uses two separate nuts fastened towards and against each other. Thus, the two nuts are bearing in opposite directions on the threads creating the "jam" effect.

How do you loosen jam nuts?

To loosen jam nuts, you can either take the outer nut off first and remove it like any other nut, or put a wrench on each nut and turn them in opposite directions to unfasten them from the assembly.

Why are jam nuts thinner?

Jam nuts are thinner because it helps save space when locking a pair of nuts together. The thinner size also means the jam nut exerts less overall force when fully torqued, so the standard nut can exert more force on the jam nut when they are fastened together without potentially damaging the material you're fastening to.