Flat head hex socket bolt： Structural characteristics, application scenarios, and selection guidelines

What is a Flat Head Hex Socket Bolt?

A Flat Head Hex Socket Bolt is a fastener with a 90° conical head. The screw head can be completely embedded in the workpiece surface. After installation, it remains flat and does not protrude. It has the characteristics of being beautiful, anti-hanging and collision-proof, and uniform force.

Its head has a hexagonal hole, which can be tightened or removed with a hexagonal wrench. It provides higher torque transmission capacity than traditional cross-slot countersunk screws and is more suitable for high-strength fastening applications.

Structural features of flat head hex socket bolt

90° conical head - flush with the workpiece surface after installation, improving aesthetics and safety.
Hexagonal drive - strong torque transmission capacity, suitable for high-strength fastening.
Partial or full threaded rod - adapted to different application requirements (full thread enhances locking force, partial thread improves connection stability).
A variety of materials are available - from ordinary carbon steel to high-strength alloy steel, stainless steel or titanium alloy to meet different working conditions.
Optional surface treatment - blackening, electroplating, Dacromet, oxidation, etc. to improve corrosion resistance and wear resistance.

Application scenarios of flat head hex socket bolt

Flat head hex socket bolt is widely used in scenarios that require flatness, beauty and strong fastening force due to its head being flush with the workpiece after installation, including:

1. Mechanical equipment & machine tool manufacturing

Applicable to scenarios such as equipment housing, guide rail fixing, mold assembly, etc., to ensure that there are no protrusions on the surface and reduce safety hazards.

Use 12.9 grade alloy steel + blackening treatment to enhance fatigue resistance.

2. Automobile & Rail Transit

Used in automobile chassis, brake discs, seat fixings and other parts, high strength and not easy to loosen are required.

High-strength alloy steel + Dacromet treatment is used to improve corrosion resistance and impact resistance.

3. Molds & Precision Instruments

Applicable to injection molds, stamping molds, CNC machine tools, etc., requiring no protrusion after installation to avoid affecting processing accuracy.

42CrMo+ surface nitriding is selected to improve wear resistance and service life.

4. Aerospace & Electronic Products

Electronic equipment housings, drone frames, aviation structural parts, etc. require lightweight and highly reliable fastening solutions.

Titanium alloy (TC4) + PVD coating is used to ensure strength while reducing weight and improving corrosion resistance.

5. Woodworking & Furniture Manufacturing

Applicable to solid wood furniture, cabinets, and decorative panels. The surface is smooth after installation and does not affect the appearance.

304 stainless steel + brushed polishing is selected to ensure rust prevention and aesthetic effects.

Structural features of flat head hex socket bolt

1. Raw material selection

Carbon steel (4.8/8.8/10.9/12.9) - Suitable for mechanical structures and general equipment.

Stainless steel (304/316) - Suitable for anti-corrosion environments, such as outdoor, chemical equipment, etc.

Alloy steel (42CrMo, SCM435) - Suitable for high-strength, impact-resistant applications, such as automobiles and machine tools.

Titanium alloy (TC4) - Suitable for lightweight and high-end applications, such as aerospace, medical equipment, etc.

2. Cold heading

Use a multi-station cold heading machine for one-time forming to ensure the integration of the head and the rod and improve the strength of the bolt.

3. Turning & threading

Use CNC precision turning to ensure the head angle and dimensional tolerance.

The thread adopts rolling technology to improve the surface finish and fatigue resistance.

4. Heat treatment

Quenching and tempering treatment (quenching + tempering) to improve strength and toughness, suitable for bolts of grade 8.8 and above.

Solution treatment, used for stainless steel bolts, to improve corrosion resistance.

5. Surface treatment

Blackening treatment: Enhance rust resistance, suitable for indoor equipment.

Galvanizing (blue and white zinc/color zinc/black zinc): Suitable for mechanical equipment with general anti-corrosion requirements.

Dacromet: Strong salt spray resistance, suitable for long-term outdoor environments such as automobiles and bridges.

Oxidation treatment: Improve the high temperature and corrosion resistance of bolts.

PVD coating (for titanium alloy): Enhance wear resistance and reduce friction coefficient.

6. Quality inspection

Dimension inspection: bolt length, head angle, thread accuracy.

Strength inspection: tensile test, hardness test, torsion test.

Surface inspection: salt spray test, wear test.

Industry standards for flat head hex socket bolts

ISO 10642 - International standard for flat head hex socket bolts, specifying metric dimensions and tolerances.
GB/T 70.1 - Chinese national standard, covering the specifications and performance of metric flat head hex socket bolts.
DIN 7991 - German standard, suitable for high-strength countersunk bolts in the machinery and mold industries.
ANSI/ASME B18.3 - American standard, suitable for British countersunk bolts.

How to choose a suitable flat head hex socket bolt?

1. Choose the right material

Ordinary equipment: carbon steel (grade 8.8/grade 10.9) + galvanized or blackened.

High strength requirements: alloy steel (grade 12.9) + quenching and tempering.

Anti-corrosion requirements: 304/316 stainless steel + polishing or Dacromet coating.

Lightweight requirements: titanium alloy + PVD coating.

2. Choose the right specifications

Determine the head angle, thread size and length according to ISO 10642 / GB 70.1 / DIN 7991.

Choose full thread or partial thread to meet different installation requirements.

3. Determine the surface treatment

Indoor environment: blackening, electroplating zinc.

Outdoor environment: Dacromet, electroplating nickel.

High temperature conditions: PVD coating or oxidation treatment.

Flat head hex socket bolts have an important position in the fields of machinery manufacturing, automobile industry, mold processing, etc. due to their advantages such as high torque, flat installation, beautiful appearance and safety.

When choosing, you should ensure the best fastening performance and durability based on strength requirements, environmental factors and surface treatment methods.

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