Detailed Explanation of Fastener Core – Bolts (Including Material/Strength/Process)

Detailed Explanation of Bolts

I. Basic Definition

A bolt is a standard fastener with external threads that needs to be used with a nut, serving to detachably connect two or more components.

Features: High strength, easy installation, reusable disassembly, and reliable connection.

II. Basic Structural Components

Structural Part	Description
Thread	Used to screw into nuts or internally threaded holes for locking purposes Divided into fully threaded and partially threaded structures
Unthreaded Shank	The unthreaded part bears shear force to enhance structural strength
Head	Used to apply torque Common shapes: Hexagonal head, flange head, round head, socket head cap, etc.
Tip	Flat or chamfered design, facilitating installation alignment

III. Common Types and Characteristics

Bolt Name	English Name	Feature Description	Application Scenarios
Hexagonal Head Bolt	Hex Bolts	The most common type with a hexagonal head, suitable for tightening with a wrench	Mechanical structures, construction installation
Flange Bolt	Hex Flange Bolts	Equipped with a washer – like flange face to increase force – bearing area and prevent loosening	Automobiles, heavy – duty equipment
Square Head Bolt	Square Head Bolts	Has a square head for easy clamping and locking, suitable for old – style structures	Railways, maintenance of old equipment
Cup Head Square Neck Bolt (Carriage Bolt)	Cup Head Bolts / Carriage Bolts	Round head with a square neck to prevent rotation, mostly used in wood structures	Woodworking connections, furniture
Countersunk Head Bolt	Countersunk Head Bolts	Tapered head that can sink into the surface of connected objects without protruding	Precision equipment, thin plate connections
Eye Bolt	Eye Bolts	Features a ring at the top for lifting or traction	Lifting devices, transportation hanging points
T – head Bolt	T – head Bolts	T – shaped head that can be embedded into T – slots	Aluminum profile structures, fixture systems
U – bolt	U – bolts	U – shaped with threads at both ends, used to clamp round pipes or rods	Pipeline fixing, vehicle chassis
Bent Anchor Bolt	Bent Anchor Bolts	One end is bent and embedded in concrete, and the other end is connected to equipment	Fixing of building foundations
Straight Anchor Bolt	Anchor Bolts	Connected to equipment flanges after being embedded in concrete	Foundation installation, equipment anchoring
Wheel Bolt	Wheel Bolt	Specifically designed for connecting wheels and wheel hubs, requiring high strength	Automobiles, engineering machinery
Hexalobular Head Bolt	Hexalobular Head Bolts	Hexalobular (Torx®) head for slip – resistance and high torque	Automobiles, electronic products
12 – Point Head Bolt	12 – Point Head Bolt	12 – point head design, compatible with special sockets, suitable for high – precision and high – torque connections	Engines, aerospace, racing cars

IV. Materials

Material	Characteristics	Typical Applications
Carbon Steel (C45, Q235, 35#)	Low cost, easy to process	General – purpose connectors
Alloy Steel (40Cr, 35CrMo)	High strength	Engineering machinery
Stainless Steel (304, 316)	Corrosion – resistant, aesthetically pleasing	Food, pharmaceutical, marine engineering equipment
Titanium Alloy	Ultra – light, high corrosion resistance	Aerospace, deep – sea engineering

Note: Stainless steel marking such as A2 – 70 means austenitic 304 stainless steel with a tensile strength of ≥ 700 MPa.

V. Mechanical Properties

Carbon steel strength grades (common standard: ISO 898 – 1):

Grade	Tensile Strength (MPa)	Yield Strength (MPa)
4.8	400	320
8.8	800	640
10.9	1000	900
12.9	1200	1080

Calculation rule:

• First digit × 100 = Tensile strength
• Second digit × First digit = Yield strength

VI. Surface Treatment Methods

Surface Treatment	Features	Application Scenarios
Galvanizing (White Zinc / Blue – white Zinc)	Corrosion – resistant, cost – effective	Indoor applications
Hot – Dip Galvanizing	Thick coating, durable	Outdoor, steel structures
Black Oxide Coating (Blackening)	Rust – proof, aesthetically pleasing	Mechanical equipment
Dacromet	High corrosion resistance (up to 1000 hours of salt spray test)	Automobile chassis, heavy industry
Nickel Plating, Chrome Plating	Highly decorative	Household appliances, electronic products

VII. Standards and Marking

• International Standards: ISO, DIN, ANSI, JIS, GB (China National Standard)

Example: DIN 933 (fully threaded hexagon head bolt)

• Thread Standards:
  • Metric (M): M6, M8, M10…
  • Imperial (UNC/UNF): 1/4″, 5/16″, 3/8″…
• Marking Method (Stamping):
  • Mark the strength grade (e.g., 8.8) and manufacturer code.
  • Stainless steel bolts are marked with A2/A4 + grade.

VIII. Brief Introduction to Manufacturing Processes

1. Cold Heading Forming: Commonly used for mass – produced bolts, featuring high speed and high material utilization rate.
2. Hot Forging Forming: Applied to high – strength and large – size bolts, ensuring more stable mechanical properties.
3. Thread Rolling: Threads are formed by extrusion, which is tougher than cutting.
4. Heat Treatment: Quenching and tempering processes to improve strength and toughness.
5. Surface Treatment: For rust prevention, corrosion resistance, decoration, etc.

IX. Common Usage Problems and Suggestions

Problem	Suggestion
Bolt Thread Stripping	Use appropriate torque and avoid repeated assembly and disassembly
Bolt Loosening	Add lock washers, threadlocker, or spring washers
Surface Rusting	Select stainless steel materials or adopt Dacromet treatment
Difficult Installation	Check hole diameter/thread matching and perform lubrication treatment

X. Practical Application Examples

1. Building steel structure connectors (M20 hot – dip galvanized bolts)
2. Automobile engine fixing bolts (Grade 10.9 high – strength bolts)
3. Stainless steel furniture connectors (304 socket head cap bolts)
4. Pipeline flange bolts (stud bolts + nuts + washers)

If you are looking for suitable bolts and nuts, please visit us here https://hktl-fastener.com/bolts-and-nuts/.