Comprehensive Guide to Fastener Basics

Fasteners are fundamental mechanical components that enable reliable connections between two or more parts. They are widely used in building structures, machinery manufacturing, electrical equipment, and new energy systems. Their core value lies in achieving controllable connections, disassembly (in some types), and structural stability.

 

 

 

From an engineering application perspective, fasteners are generally classified into the following 12 categories:

 

1. Bolts

Composed of a head and a threaded shank, they require a nut for use. Suitable for through-hole connections, they are typical disassembly connections. Common products include Hex Bolts and Flanged Hexagon Head Bolt Screws, widely used in steel structures and equipment installation.

 

2. Studs

Headless structures with external threads at both ends. One end screws into the nut, and the other end is secured with a nut. Suitable for high-intensity or frequent disassembly scenarios.

 

3. Screws

Can be screwed directly into threaded holes or used with nuts. Based on construction, they include:

Machine Screw with Phillips Head

Pan Head Screw (Stainless Steel)

Countersunk Flat Head Screws

Stainless steel pan head screws are suitable for corrosion-resistant environments.

 

4. Nuts

Internal threaded fasteners that form a complete connection pair with bolts or studs, such as:

M10 304 Stainless Steel Hex Bolt Screw Nut Flat Washer Combination

 

5. Self-tapping Screws

They form their own internal threads within the material and are commonly used for thin sheet metal connections, such as:

Stainless steel sheet metal screws

 

6. Wood Screws

Specifically designed for wood structural connections, they have deep threads and a large lead.

 

7. Washers

Used to distribute loads, prevent loosening, or protect contact surfaces, such as spring washers and flat washers. 8. Retaining Rings

Used in shafts or holes to restrict axial movement of parts.

 

9. Pins

Used for positioning or load transfer.

 

10. Rivets

Form a permanent, non-removable connection.

 

11. Assemblies

Pre-assembled fasteners, such as:

Bolt + Washer Combination (Hexagon Head Machine Screw Metric Thread Flat Spring Lock Washer Bolt 304 Stainless Steel)

12. Weld Studs

Fixed onto the base material by welding for subsequent assembly.

 

 

 

1. Functions of Threads

Threads are the core structure of fasteners, primarily serving the following functions:

Fastening connections
Force transmission
Sealing connections (pipe threads)

Their advantages lie in their simple structure, high reliability, and ease of assembly and disassembly.

 

2. Thread Classification

(1) Classification by Application

Ordinary Threads (for fastening): Triangular tooth profile, most widely used

Transmission Threads: Trapezoidal, rectangular, etc.

Sealing Threads: Pipe Threads

Special Threads

(2) Classification by Standard System

Metric Thread

Unified Thread (British/American)

 

3. Key Terms

Major Diameter

Minor Diameter

Pitch Diameter – determines fit performance

Pitch

Thread Angle

Left-hand/Right-hand

 

 

1. Inspection Methods

Common inspection tools include:

Thread ring gauge (external thread)

Thread plug gauge (internal thread)

Used to simulate assembly conditions for qualification judgment.

 

2. Pitch Diameter Measurement

The pitch diameter directly affects the fit performance. Common methods include:

Three-needle method; Pitch micrometer

 

3. Thread Fit Grades

(1) Imperial System

1A/1B: Loose fit

2A/2B: General fit

3A/3B: High precision

(2) Metric System

Common combinations:

6H/6g (Standard fit)

6G/6e (Thick coating)

4H/4h (High precision)

 

 

The fastener material directly determines its mechanical properties and environmental resistance.

 

1. Common Materials

Carbon Steel (High Strength, Low Cost)

Stainless Steel (Corrosion Resistant)

Alloy Steel (High-Strength Applications)

Typical Products:

M6 Hexagon Socket Head Screw 304 Stainless Steel Knurling
Flat-head Hexagon Socket Stainless Steel Screws

 

2. Heat Treatment Requirements

Including:

Quenching
Temperature Hardening

Used to improve:

Tensile Strength
Fatigue Life
Wear Resistance

 

3. Mechanical Performance Indicators

Key Parameters:

Tensile Strength
Yield Strength
Hardness

 

 

 

1. Steel Structure Connections

Commonly used high-strength bolt connections, emphasizing:

Preload Control
Friction-type Connections

 

2. Electrical and Connection Terminals

Examples:

M10 Clamp Wire Terminal
M8 Socket Head Cap Screws Terminal with Spacer

Used for conductive connections and structural fixation.

 

3. Precision Equipment

Usage:

Set Screw with Hollow Head Bolt Base for position locking and fine-tuning.

 

 

In engineering procurement and design, the following parameters should be given special attention:

 

Connection type (removable)

Load type (static/dynamic)

Environmental conditions (corrosion, temperature)

Assembly space limitations

Standards and certification requirements

 

Basic general-purpose products such as steel screws can meet routine needs, while stainless steel or high-strength grade products should be prioritized in high-reliability scenarios.

 

 

Although fasteners are basic components, their design, selection, and application directly affect the safety and reliability of the overall structure. From classification systems and thread principles to material properties and fit grades, each aspect involves clear engineering logic. For procurement personnel and engineering technicians, mastering this basic knowledge is key to achieving efficient selection and quality control.