What is the purpose of a screw nut?

nut, in technology, fastening device consisting of a square or hexagonal block, usually of metal, with a hole in the centre having internal, or female, threads that fit on the male threads of an associated bolt or screw. A bolt or screw with a nut is widely used for fastening machine and structural components.

In addition to the standard square and hexagonal nuts, there are many special types. Several are illustrated in the Figure, including the slotted or castellated nut; when this nut is tightened on the bolt, the slots are aligned with a hole in the bolt and locked in place by a cotter pin or wire lacing to prevent loosening or unscrewing. Locking can also be accomplished by tightening a thin nut called a jam nut against a standard nut. Another locknut contains a fibre or plastic insert near the top of the nut; locking occurs when this insert interferes with the bolt threads as the nut is tightened. The wing nut is used in applications in which frequent adjustment is necessary and hand tightening is sufficient.

Self-retained nuts provide a strong, permanent fastener for many types of thin materials; they are threaded blocks held in special enclosures attached to the part by welding, rivetting, screwing, or snap-on attachments. Single-thread nuts are formed by stamping a thread-engaging impression in a piece of flat metal.

Type of fastener with a threaded hole

A nut is a type of fastener with a threaded hole. Nuts are almost always used in conjunction with a mating bolt to fasten multiple parts together. The two partners are kept together by a combination of their threads' friction (with slight elastic deformation), a slight stretching of the bolt, and compression of the parts to be held together.

In applications where vibration or rotation may work a nut loose, various locking mechanisms may be employed: lock washers, jam nuts, eccentric double nuts,[1] specialist adhesive thread-locking fluid such as Loctite, safety pins (split pins) or lockwire in conjunction with castellated nuts, nylon inserts (nyloc nut), or slightly oval-shaped threads.

Square nuts, as well as bolt heads, were the first shape made and used to be the most common largely because they were much easier to manufacture, especially by hand. While rare today[as of?] due to the reasons stated below for the preference of hexagonal nuts, they are occasionally used in some situations when a maximum amount of torque and grip is needed for a given size: the greater length of each side allows a spanner to be applied with a larger surface area and more leverage at the nut.

The most common shape today is hexagonal, for similar reasons as the bolt head: six sides give a good granularity of angles for a tool to approach from (good in tight spots), but more (and smaller) corners would be vulnerable to being rounded off. It takes only one sixth of a rotation to obtain the next side of the hexagon and grip is optimal. However, polygons with more than six sides do not give the requisite grip and polygons with fewer than six sides take more time to be given a complete rotation. Other specialized shapes exist for certain needs, such as wingnuts for finger adjustment and captive nuts (e.g. cage nuts) for inaccessible areas.

Types

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A wide variety of nuts exists, from household hardware versions to specialized industry-specific designs that are engineered to meet various technical standards. Fasteners used in automotive, engineering, and industrial applications usually need to be tightened to a specific torque setting, using a torque wrench. Nuts are graded with strength ratings compatible with their respective bolts; for example, an ISO property class 10 nut will be able to support the bolt proof strength load of an ISO property class 10.9 bolt without stripping. Likewise, an SAE class 5 nut can support the proof load of an SAE class 5 bolt, and so on.

Locknuts

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Many specialised types of nut exist to resist loosening of bolted joints, either by providing a prevailing torque against the male fastener or by gripping against the bolted components. These are generally referred to as locknuts.

Gallery

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• Left to right: Wing, hex, hex flange, and slab weld nuts.

• Left to right: Slotted, square (upper), T-nut (lower), cap (or acorn), nylon locking (top and side views), and castellated nuts.

• Hexagon nuts.

Standard nut sizes

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Metric hex nuts

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Note that flat (spanner or wrench) sizes differ between industry standards. For example, spanner or wrench sizes of fastener used in Japanese built cars comply with JIS automotive standard.

SAE hex nuts

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5

32

5

32

3

16

3

16

1

4

5

16

11

32

3

8

7

16

1

4

1

4

7

16

5

16

5

16

1

2

3

8

3

8

9

16

7

16

7

16

11

16

1

2

1

2

3

4

9

16

9

16

7

8

5

8

5

8

15

16

3

4

3

4

1

+

1

8

7

8

7

8

1

+

5

16

1

+

1

2

Classifications

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Hex nuts, recognized by their six-sided shape, and square nuts, with a square form, are commonly used. Steel nuts are strong and great for construction, while stainless steel ones resist rust, perfect for outdoor use. Brass nuts, corrosion-resistant, find their place in electrical and plumbing work. Lock nuts, like nylon-insert or prevailing torque types, prevent loosening due to vibration or torque, catering to specific needs across industries.

Manufacture

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The manufacturing process of nuts involves several steps. It begins with the selection of raw materials like steel, stainless steel, or brass, depending on the desired type of nut. The chosen material undergoes heating to make it more malleable, followed by forming or forging processes to create the basic shape of the nut. Threads are then cut or formed onto the nut using specialized machinery. After threading, nuts may undergo additional treatments such as heat treatment or surface finishing to enhance their strength, durability, or appearance. Quality control checks are performed throughout the manufacturing process to ensure that the nuts meet industry standards and specifications.

• Nut blanking

• Nut threading

See also

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References

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Bibliography

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