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Nut (hardware)

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A nut is a specialized type of fastener featuring a threaded hole.

Square nuts from Ace Hardware, Concord MA
Square nuts from Ace Hardware, Concord MA

It is designed to work in conjunction with a mating bolt to secure multiple parts together. This connection is vital in everything from household repairs to massive infrastructure projects. By threading the nut onto a bolt, the two components create a strong, mechanical bond. This process allows engineers to join complex assemblies with great precision and strength.

The mechanism that holds a nut and bolt together relies on several physical principles. As the nut is tightened, the threads of the nut rub against the threads of the bolt. This creates friction, which prevents the parts from sliding apart. At the same time, the bolt undergoes slight elastic deformation, meaning it stretches just a tiny amount. This stretching, combined with the compression of the parts being held, creates a constant clamping force. This force ensures the assembly remains stable and secure under load.

Nuts come in many different shapes, each serving a specific mechanical purpose. The most common shape is the hexagonal nut, which has six sides. This geometry allows a tool to approach from various angles, making it useful in tight spaces. If a nut had many more sides, the corners might be too fragile and round off easily. Square nuts were the first common shape because they were easier to manufacture by hand. Today, they are used when a larger surface area is needed to provide more leverage or grip.

Square nuts from Ace Hardware, Concord MA
Square nuts from Ace Hardware, Concord MA

Other specialized types include wingnuts for finger adjustment and cage nuts for inaccessible areas.

Wingnut-hardware
Wingnut-hardware
Kafigmutter
Kafigmutter

Historically, nuts and bolts were not interchangeable. In the past, they were handcrafted together so that one specific nut matched one specific bolt. If a fastener was lost or damaged, it was nearly impossible to find a replacement. In 1841, Joseph Whitworth proposed that a standard system should be established. This became critical during the construction of the Crystal Palace for the Great Exhibition of 1851 in London. The firm Fox Henderson used standardized nuts and bolts to build the structure in only 190 days. This success led to the widespread adoption of standardized sizing.

SydneyHarbourBridgeNutMilsonsPoint
SydneyHarbourBridgeNutMilsonsPoint

To prevent loosening caused by vibration or rotation, engineers use various locknuts. These are specialized fasteners designed to resist movement. A Nyloc nut, for example, uses a nylon insert to provide grip.

Domed cap nut
Domed cap nut

Other methods include using jam nuts, lock washers, or even specialized adhesive thread-locking fluids like Loctite. Some designs, such as the HARDLOCK nut, use a wedge principle to eliminate space between threads.

HARDLOCK nut
HARDLOCK nut

These mechanisms ensure that critical machines do not fall apart while they are running.

Nuts are also categorized by their material and strength ratings. Steel nuts are highly durable and used in heavy construction. Stainless steel is chosen for its ability to resist rust in outdoor environments. Brass nuts are often used in electrical or plumbing work because they resist corrosion. In industrial settings, nuts are graded to match the strength of their bolts. For instance, an ISO property class 10 nut is strong enough to support an ISO property class 10.9 bolt without stripping the threads.

Nut marking Metric Class 10 9
Nut marking Metric Class 10 9

The manufacturing process for a nut involves several precise steps. It begins with selecting a raw material like steel or brass. The metal is then heated to make it more malleable, which means it is easier to shape. The material undergoes forging to create the basic outer form. Next, specialized machinery is used to cut or form the threads inside the hole. Finally, the nut may receive a heat treatment or a surface finish to improve its strength or appearance. This ensures the final product meets strict international standards like ISO or DIN.

Nut marking SAE Grade 8
Nut marking SAE Grade 8
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🖼️ Images & Media (30)
File:M4 Inbusschraube focusstacked.jpg
M4 Inbusschraube focusstacked.jpg
File:SydneyHarbourBridgeNutMilsonsPoint.JPG
SydneyHarbourBridgeNutMilsonsPoint.JPG
File:Domed_cap_nut.jpg
Domed_cap_nut.jpg
File:Quergewindebolzen_QD-M6-7,5-13x16,2.jpg
Quergewindebolzen_QD-M6-7,5-13x16,2.jpg
File:Kafigmutter.jpg
Kafigmutter.jpg
File:Two spire clips.jpg
Two spire clips.jpg
File:Coupling_Nut.svg
Coupling_Nut.svg
File:Serrated hex flange nut.jpg
Serrated hex flange nut.jpg
File:HARDLOCK nut.PNG
HARDLOCK nut.PNG
File:Rampamuffe_(klein).jpg
Rampamuffe_(klein).jpg
File:Knurled nuts, Lexington MA.jpg
Knurled nuts, Lexington MA.jpg
File:Blindnietmutter.jpg
Blindnietmutter.jpg

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