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China Suppliers Factory Black Zinc Oxide CSK Flat Head Hexagonal Bolt Screw – Carbon Steel, Alloy Steel, Stainless Steel
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China Suppliers Factory Black Zinc Oxide CSK Flat Head Hexagonal Bolt Screw – Carbon Steel, Alloy Steel, Stainless Steel

●  FOB Price: US $0.4 - 9.99 per Piece
●  Minimum Order Quantity: 100 Pieces
●  Supply Capacity: 10,000 Pieces per Month
●  Surface Treatment: Black Oxide
●  Material Options: Carbon Steel, Alloy Steel, Stainless Steel
●  Standards: DIN, GB, UNC, BSW, JIS, and more
●  Certifications: ISO9001, ISO14001, ISO45001, SGS
●  Grades Available: 4.8, 8.8, 10.9, 12.9, A2-70, A4-70, A4-80, and others

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As a leading China supplier and factory, we specialize in high-quality fasteners made from durable materials. Our products, including a variety of grades and surface treatments, meet international standards and come with reliable certifications. With a robust supply capability, we can fulfill large orders promptly, ensuring you receive the products you need for your projects.

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    Product Detail

    Structure and Characteristics

    Head Design

    Flat Head: The top surface of the head is flat and can be aligned with the surface of the workpiece after installation, reducing protrusions and suitable for occasions that require a flat or streamlined appearance.

    Conical bottom surface: The bottom surface of the head is usually conical and can be embedded into the pre made conical counterbore of the workpiece to provide better fit.

    Hexagonal Drive

    The hexagonal groove in the center of the head (ISO 4762 standard) can fully fit with the internal hexagonal wrench, transmitting large torque and reducing the risk of slipping.

    Threaded Section

    The thread types are mostly metric coarse teeth (such as M4, M6) or fine teeth (such as M8 × 1.25), and the length and diameter can be customized according to needs.

    Main application scenarios

    ⚙️Mechanical Manufacturing

    Used for the assembly of precision equipment (such as machine tools and molds), in areas that require high loads and limited space.

    🚗Automotive Industry

    Requires highly reliable connections for engine components, transmissions, chassis, and other components.

    💻Electronic Products

    The structural fixation of compact devices such as laptops and mobile phones.

    ✈️Aerospace

    Connection points with high requirements for weight and strength in lightweight design.

    Core advantages

    High Torque Transmission

    The contact area between the hexagonal hole and the wrench is large, which can withstand greater tightening torque.

    Space Saving

    The flat head design does not occupy external space, making it suitable for small or aesthetically pleasing installation environments.

    Anti-Loosening Performance

    When used in conjunction with spring washers or thread glue, it can effectively prevent loosening caused by vibration.

    Aesthetics

    After installation, the surface is flat without exposed bolt heads, suitable for products with high appearance requirements.

    Specifications and standards

    Category Details
    Material Carbon steel (surface galvanized, blackened treatment), stainless steel (such as 304/316, corrosion-resistant), titanium alloy (lightweight and high-strength scenario).
    Size Standard Metric (ISO 4762), American (ANSI/ASME B18.3), with a common diameter range of M2 to M24.
    Surface Treatment Galvanized (rust proof), Dacromet (high-temperature corrosion resistance), electrophoretic (decorative coating), etc.
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    Frequently Asked Questions

    QWhat is a flat head socket cap screw and how does it differ from other socket cap screws?
    A flat head socket cap screw features a countersunk, flat-top head with a hexagonal drive socket that allows the head to sit flush with or below the workpiece surface after installation. Unlike cylindrical-head or button-head socket cap screws, its conical underhead geometry mates precisely with a matching counterbore, creating a seamless surface finish ideal for appearance-sensitive or space-constrained applications.
    QWhat materials are flat head socket cap screws commonly manufactured from?
    The three most common materials are carbon steel (typically zinc-plated or black-oxide treated for corrosion protection), stainless steel grades 304 and 316 (preferred for corrosive or wet environments), and titanium alloy (used when both minimal weight and high tensile strength are required, such as in aerospace and high-performance motorsport applications).
    QWhich international standards govern flat head socket cap screws?
    Metric flat head socket cap screws are defined by ISO 10642, with hexagonal socket geometry covered under ISO 4762. Inch-series versions follow ANSI/ASME B18.3 for North American manufacturing. Both standards specify dimensional tolerances, mechanical properties, and material grades, ensuring interchangeability across global supply chains with a typical diameter range of M2 to M24.
    QWhat is the difference between coarse-thread and fine-thread flat head socket cap screws?
    Coarse-thread variants (e.g., M6 × 1.0) assemble faster, tolerate minor thread damage better, and suit most general-purpose applications. Fine-thread variants (e.g., M8 × 1.25) provide a larger stress area for higher tensile load capacity, allow more precise torque control, and resist vibration-induced loosening more effectively — making them preferable for precision machinery, thin-walled materials, and high-vibration environments.
    QHow can I prevent flat head socket cap screws from loosening under vibration?
    Effective methods include applying a medium-strength thread-locking adhesive (such as Loctite 243), using spring washers or serrated lock washers beneath the screw head, or selecting screws with an integrated nylon-patch self-locking feature. Proper installation torque is equally critical — under-tightening is one of the most common causes of vibration-induced loosening even when locking aids are already in use.
    QWhat surface treatments are available and how do I choose the right one?
    Galvanized — economical general-purpose rust protection for indoor or light outdoor use. Dacromet — outstanding resistance to high-temperature and salt-spray corrosion, widely specified for automotive underbody and exhaust components. Electrophoretic coating — a smooth, decorative finish well-suited to consumer electronics and visible hardware. For marine, food-processing, or chemically aggressive environments, stainless steel 316 or titanium is the most reliable long-term choice.