Hexagonal Nut

Size and shape
Square nuts have a square shape with four equal sides and right angles.
Hex nuts have a hexagonal shape with six sides.

Compatibility with fasteners and tools
Square nuts are typically used with bolts or screws that have square heads, requiring specialized tools like square socket wrenches or pliers for installation and removal.
Hex nuts are compatible with a wide range of fasteners, such as bolts, screws, or threaded rods, and can be easily tightened or loosened using standard wrenches or socket sets.

Strength and stability
Square nuts provide a secure and stable connection due to their anti-rotation feature, making them resistant to loosening caused by vibration or torque.
Hex nuts also offer reliable strength and stability, with the six-sided design providing multiple contact points for a tight connection.

Ease of installation and removal
Square nuts may be more challenging to install or remove in tight or hard-to-reach spaces due to their square shape and the need for specialized tools.
Hex nuts are generally easier to install and remove, as they can be tightened or loosened using standard wrenches or socket sets, offering greater accessibility.

Cost and availability
The cost and availability of square nuts may vary depending on the specific size, material, and finish. They may be slightly less commonly available compared to hex nuts in certain hardware stores.
Hex nuts are widely available and commonly stocked in hardware stores, making them more accessible and generally more cost-effective.

Step 1: Lubricate the Hex-nut
The nut is probably stuck because of rust, so spraying it with some kind of lubricant would help release it. I recommend either WD-40 or PTFE, but grease or vaseline might also work.

Step 2: Add 2 More Hex-nuts, & Tighten
I screwed on two hex-nuts on the other side of the threaded rod, and tightened them together with pliers. This needs to be tight, but there is no need to overtighten. See the pictures for more information.

Step 3: Clamp the Hex-nuts in a Vise, & Remove the Nut
I clamped both hex-nuts in my vise, as shown in picture 1. Now, guess what? I clamped my big locking pliers onto the nut, and turned. The more force you apply, the stronger the force which stops the hex-nuts that are clamped in the vise from moving. I used a vise, but you can also use locking pliers, which work just a well

Step 4: Unscrew Both Hex-nuts
All you have to do now, is to unscrew the two hex-nuts that were screwed on in step 2. You can see the second picture to see how that's done.

Regular Cleaning and Lubrication
Over time, dirt, grime and rust can accumulate on nuts and bolts, leading to corrosion and making them difficult to remove or adjust. Regular cleaning can help prevent these issues. Start by removing any visible dirt or debris using a wire brush or a similar tool. Soak the nuts and bolts in warm water and mild detergent for a more thorough cleaning. After soaking, scrub them gently with a brush to remove any remaining residue. Rinse thoroughly and dry them completely to prevent rust formation.
Once cleaned, apply a suitable lubricant to the nuts and bolts. This helps reduce friction, making it easier to tighten or loosen them when needed. A light coat of machine oil or a specialised fastener lubricant will suffice. Make sure to wipe off any excess lubricant to prevent attracting more dirt.

Appropriate Storage Solutions
Proper storage of nuts and bolts can significantly extend their lifespan and maintain their integrity. Store nuts and bolts in a dry, cool place away from direct sunlight and moisture. Excessive humidity can lead to rust, while extreme temperatures can affect the metal's strength. Use airtight containers or resealable plastic bags to keep them dry and dust-free.
Organise your nuts and bolts by size, type and material. This will make it easier to find the right fastener when needed and prevent the mixing of different metals, which can lead to corrosion. Labelled bins or drawers can also help keep your collection organised and easily accessible.

Routine Inspections for Wear and Damage
Routine checks can help ensure the safety and reliability of your fasteners. Inspect your nuts and bolts at regular intervals, depending on the frequency of use and the conditions they are exposed to. More frequent inspections might be necessary for critical applications.
Look for signs of wear, such as rust, corrosion, stripped threads or deformation. If any damage is detected, replace the affected nuts and bolts immediately to maintain the integrity of your assembly. Pay special attention to high-stress areas where fasteners are more likely to experience wear.

Careful Handling
Always use the appropriate size and type of wrench or socket for your nuts and bolts. Using the wrong tools can strip threads or cause the fasteners to become rounded, making them difficult to work with. For particularly stubborn nuts and bolts, consider using penetrating oil and a breaker bar to avoid excessive force that could damage the fastener.
When installing nuts and bolts, ensure you are not over-tightening or under-tightening them. Over-tightening can lead to stripped threads or broken bolts, while under-tightening can result in loose assemblies. Using a torque wrench can help you apply the correct amount of force as specified by the manufacturer.

Buy Metric and Standard Gauges for Nut Measuring
Thread gauges for bolts and screws are very different instruments from those used to measure nuts. The reason why is that a gauge for nuts has to go inside the nut and fit inside the opening of the nut to measure it properly, whereas the gauge for a bolt or screw only has to measure on the outside where the threads are. The gauges for nuts look more like socket wrenches where the heads of these tools are inserted into and screwed into the nut to find the right fit. When you do this, and you find the right fitting gauge, the measurement of that gauge is imprinted on the handle so that you know what the measurement of the nut is.

Pick up a Hex Nut and a Gauge That Looks Like It Would Be a Good Fit
Pick up a hex nut of any size. Look at your set of nut gauges. Pick out the few that look as though they might fit inside the hex nut. Test each one, attempting to screw the gauge into the nut. You want it to fit exactly right without being too loose or forced. When you find the one that fits the nut perfectly, turn the gauge over in your hand to look at the measurement indicated on the handle of the gauge. It will tell you the exact measurement of the threads inside the nut. This will also tell you exactly what the thread gauge is on the screw or bolt that is supposed to accompany this nut.

How It Is Useful and Why You Would Want to Do This
In industrial settings, there are thousands of nuts, bolts, and screws. When they come loose from machinery or equipment and/or need to be replaced, it is not as though you know automatically what to buy. You need these gauges to tell you the correct fitting and size of the fasteners so that everything fits back together perfectly.

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