Nuts are indispensable fasteners in mechanical connections, primarily used with bolts and screws with external threads to form secure connections. Nuts come in various types and sizes, suitable for a wide range of industrial and everyday applications. This article provides a detailed introduction to the definition, classification, composition, performance, selection principles, and application fields of nuts.

I. Definition of Nuts

A nut is a fastener with internal threads that mates with a bolt or screw with external threads. Through the engagement of the threads, nuts can tightly secure two or more parts together, forming a reliable fastening structure. Nuts are widely used in mechanical manufacturing, construction engineering, the automotive industry, and household appliances.

II. Classification of Nuts

1. Classification by Shape

  • Hex Nuts: The most common type, with a hexagonal shape, suitable for most mechanical and engineering connections.
  • Square Nuts: With a square shape, commonly used in wood structures and connections that require anti-rotation.
  • Round Nuts: With a round shape, suitable for applications with high aesthetic requirements.
  • Wing Nuts: With two wing-like projections, easy to tighten and loosen by hand, suitable for connections that require frequent adjustments.

2. Classification by Function

  • Standard Nuts: Used for general mechanical and structural connections.
  • Lock Nuts: With anti-loosening features, suitable for vibrating environments, such as nylon insert lock nuts and metal lock nuts.
  • Flange Nuts: With a flange at the base, increasing the contact area and providing greater fastening force.
  • Cap Nuts: With a closed top to protect the end of the bolt, preventing corrosion and damage.

3. Classification by Material

  • Carbon Steel Nuts: High strength and low cost, suitable for most conventional applications.
  • Stainless Steel Nuts: Strong corrosion resistance, suitable for damp or corrosive environments.
  • Copper Nuts: Excellent electrical and thermal conductivity, suitable for electrical and electronic applications.
  • Plastic Nuts: Lightweight and corrosion-resistant, suitable for chemical environments or light-load applications.

4. Classification by Thread Type

  • Metric Nuts: With metric threads, widely used globally in industrial applications.
  • Imperial Nuts: With imperial threads, mainly used in North America.
  • Fine Thread Nuts: With smaller thread pitch, suitable for precise adjustment connections.
  • Coarse Thread Nuts: With larger thread pitch, suitable for quick fastening connections.

III. Composition of Nuts

1. Thread

The core component of a nut is its internal thread, which mates with the external thread of a bolt or screw. The design and precision of the internal threads directly affect the nut's fastening performance and service life.

2. Head

Nuts come in various head shapes, including hexagonal, square, and round. The head design primarily considers ease of operation and connection strength.

3. Base

Some special nuts, such as flange nuts, have a flange at the base, increasing the contact area and improving fastening force and anti-loosening performance.

IV. Performance of Nuts

1. Fastening Force

Fastening force is a crucial performance indicator of nuts, determining the strength of the connection. It depends on the thread design, material, and size of the nut. High-strength nuts usually offer greater fastening force, suitable for load-bearing connections.

2. Anti-Loosening Performance

Anti-loosening performance is the ability of a nut to maintain fastening force under vibration or impact. Lock nuts enhance anti-loosening performance through mechanical or chemical methods, suitable for high-vibration environments.

3. Corrosion Resistance

Corrosion resistance determines the service life of nuts in different environments. Stainless steel and galvanized nuts offer high corrosion resistance, suitable for damp or corrosive environments.

4. Thermal Stability

Thermal stability is the ability of a nut to maintain performance in high-temperature environments. Copper and stainless steel nuts usually offer high thermal stability, suitable for high-temperature applications.

V. Principles for Selecting Nuts

1. Selection Based on Material

Different materials have different requirements for nuts. For metal materials, high-strength carbon steel or stainless steel nuts should be chosen. For electrical and electronic applications, copper nuts with good conductivity should be selected. For chemical environments or light-load applications, plastic nuts are suitable.

2. Selection Based on Application Environment

The application environment significantly impacts nut selection. Stainless steel or galvanized nuts should be chosen for damp or corrosive environments, while high-temperature-resistant nuts should be selected for high-temperature environments.

3. Selection Based on Load Requirements

Load requirements determine the specifications and type of the nut. High-strength nuts should be chosen for heavy-load connections, while standard nuts can be used for light-load connections.

4. Selection Based on Connection Type

Different connection types require different nuts. Lock nuts should be chosen for connections that need anti-loosening features, while flange nuts are suitable for connections requiring increased contact area.

5. Selection Based on Installation Conditions

Installation conditions also affect nut selection. Wing nuts or other easy-to-operate nuts should be chosen for confined spaces or manual operations.

VI. Application Fields of Nuts

1. Construction Engineering

Nuts are widely used in construction engineering for connecting steel structures, bridges, and building frames, providing high-strength and reliable fastening solutions.

2. Machinery Manufacturing

In the machinery manufacturing industry, nuts are used for assembling and securing equipment and mechanical components, ensuring structural stability and reliability.

3. Automotive Industry

In the automotive industry, nuts are used for assembling car bodies, chassis, and engine components, providing high-strength connections and ensuring the safety and durability of vehicles.

4. Aerospace

The aerospace industry has stringent quality requirements for nuts, which are used for assembling high-precision components of aircraft, spacecraft, and missiles, providing reliable fastening performance.

5. Furniture Manufacturing

Nuts are used in furniture manufacturing for connecting wooden and metal components, providing stable and aesthetically pleasing assembly results.

6. Power Industry

In the power industry, nuts are used for connecting and securing electrical equipment and transmission lines, ensuring the safety and stability of power systems.

7. Household Appliances

Nuts are used in household appliances for assembling and securing various components, ensuring the stability and safety of the appliances.


As an important fastener, nuts come in various types and have wide-ranging applications. Understanding the definition, classification, composition, performance, selection principles, and application fields of nuts is essential for improving assembly efficiency and connection quality. With technological advancements, the design and materials of nuts continue to innovate, providing better solutions for the fastening needs of various industries.

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