J-nuts are self-retaining fasteners similar to U-nuts or U-clips. Instead of having two legs the same length, the J-nut has one leg that is shorter than the other. Other types of clip-on nuts are S-nuts and cage nuts. They either snap over the edges of panels or into center hole locations and are either latched, pressed or clipped into position where they retain themselves until a fastener is received.

How do they work?

What allows J-nuts to work is the “J” shape design, which allows the nuts to attach to sheet metal panels or parts easily and quickly without the need for any tools. When the J-nut is installed, the panel that will be mated is positioned accordingly and the fastener is driven, resulting in a reliable and solid assembly.

How are they made, and how do they work?

J-nuts are typically made from a strip of spring steel that is bent into the “J” shape in order to form the two legs. The longer of the two legs features either a hole that has prongs to secure a bolt, known as a “speed nut,” or a thicker nut that is attached to the leg and has threads for the bolt to secure to. The second leg is short enough to ensure it does not affect the bolt when it is fastened.

The phrase “speed nut” refers to the prongs on the J-nut creating the thread for the bolt to attach to, instead of actual threads. This way of manufacturing a J-nut is an economical and simple approach to creating a thread and it will also act as the lock nut. The disadvantage of using this type of J-nut is that it is quite weak and will fail relatively easily if a fastener is tightened with high torque.

On the other hand, if the second version of the J-nut is used, with the pre-formed threads tapped into a much thicker nut, then it is significantly stronger. This will allow fasteners tightened with a much higher torque to be used. This type of nut can be attached to the body of the J-nut in two ways. It can be wedged between tabs that are folded from the clip itself, the advantage being that there is some float with the nut, and this can make up for some misalignment in the holes. The second method is where is the nut is swaged or spot-welded to the sheet metal to ensure an extremely secure connection. This will again allow for an even higher torque to be used when tightening fasteners.

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The ends of the J-nuts’ legs can also be flared out for lead lips, and this will allow it to easily slide over the edge of a sheet metal panel. As it slides over the edge, the legs will open, and the nut will place a slight clamping force on the sheet metal.

Torque-tension relationship model

The below equation is what estimates the amount of torque that is needed to achieve a certain clamp force when the bolt diameter is known:


T = Torque

F = Force

D = Diameter

K = Nut factor

The "nut factor" is a group of assumptions that are associated with torque measurement. It exists to make the factors that affect using torque measurement more streamlined so that a precise clamp force can be determined. Clamp force is created by its equal and opposite bolt tension.

A multitude of factors influence the torque-tension relationship, like the size, material, thread lubricants, wear of the fasteners, nuts and washers, surface finish, corrosion, plating and more. The nut factor was created to summarize all of these variables, and creates a linear model that displays the rate that tension develops when torque is applied.

Torque wrenches are used in a number of fields to ensure that the exact amount of desired torque is used. Source: Adobe/NischapornTorque wrenches are used in a number of fields to ensure that the exact amount of desired torque is used. Source: Adobe/Nischaporn

The value of the nut factor is known as an “empirical value.” This means that the values that are used for the nut factor are derived from laboratory testing and observation, rather than just theory. However, unexpected influences and unforeseen variables can creep in. This can make the nut factor unpredictable.

Benefits of using J-nuts

There is a significant number of benefits to using J-nuts for assemblies, as they eliminate the need for any welding, special tools or skills.

  • Self-retaining
  • They are universal and can be used where a bolt or screw is used
  • They eliminate the need for retapping clogged threads
  • Erosion and rustproof
  • Easily assembled with no tools
  • Parts come apart easily, makes them easily serviceable
  • They eliminate clinching and welding costs
  • No skills needed to use
  • Can be used after porcelainizing or painting
  • They correct holes that are out of line

What are J-nuts made out of?

J-nuts are typically made out of mild steel, with or without plating, but they can be made from a number of other materials as well, including copper, bronze or stainless steel.

Applications of J-nuts

J-nuts are extremely affordable, easy to manufacture and are also reusable, which makes them suitable for a wide range of applications. Some of the obvious applications would be sheet metal enclosures and assemblies, but you will find them everywhere in the assembly of vehicles, appliances, heating-ventilation- and-air conditioning systems, lawn and garden equipment, electronic equipment enclosures and installations that are hard to reach or blind assemblies.

So, what do you think of J-nuts? Do you use them in your work, and do you prefer them to other types of nuts? Engineering360 would love to hear your thoughts in the comments below!