What are the common types and specifications of hex screws

Hexagonal screws can be divided into two major categories: outer hexagonal screws and inner hexagonal screws based on their head structures and application scenarios. The following provides an explanation from the perspectives of type, specification, application scenario, and key points for selection:

1. Common types

1. Hexagonal socket head cap screw

Definition: The head is an externally convex hexagon with no internal hole, requiring the use of a wrench (such as an open-end wrench or adjustable wrench) for operation.

Features:

Strong torque transmission capacity: The hexagonal structure provides 6 force application points, making it suitable for high-strength connections.

Low cost: The manufacturing process is simple, and the price is usually half of that of hexagon socket screws.

Large space requirement: Adequate operating space is required during installation, making it unsuitable for confined environments.

Typical applications:

Mechanical equipment (such as engine block connections), building structures (steel structure bridges), and automotive chassis components.

2. Hexagonal socket screw

Definition: The head is round with an inner hexagonal hole in the middle, requiring operation with an inner hexagonal wrench (L-shaped tool).

Features:

Low head: Can be embedded into the surface of components, suitable for space-constrained scenarios.

Elegant appearance: The head is flat, commonly used in furniture, electronic devices, and other scenarios where screws need to be concealed.

Slightly lower torque: Due to structural limitations of the head, the maximum torque is usually lower than that of external hexagon screws.

Subdivision type:

Hexagon socket head cap screw: High universality, with a head diameter approximately 1.5 times the thread diameter.

Countersunk hexagon socket screw: The head is conical, allowing it to fit into a conical hole, resulting in a flush surface.

Pan head hexagon socket screw: With a rounded head, it increases the contact area with wooden materials and is commonly used in furniture.

Headless hexagon socket screw: The head is hidden, suitable for scenarios requiring tightening force or concealed installation (such as jackscrew structures).

Typical applications:

Precision instruments (such as optical equipment adjustment), electronic equipment (circuit board fixation), furniture assembly.

II. Common specifications

1. Metric specifications (M series)

Representation method: thread diameter (mm) × thread pitch (mm), such as M4×0.7, M6×1.0.

Common specifications:

Hexagon socket head cap screws: M4, M5, M6, M8, M10, M12, etc.

Hexagon socket screws: M3, M4, M5, M6, M8, etc. (usually with smaller diameters).

Length range: Varies from a few millimeters to hundreds of millimeters, and needs to be selected based on the thickness of the connected parts.

2. Imperial specifications

Representation method: In inches, such as #4-40, #6-32, #8-32, etc. (The number represents the thread diameter, and the suffix indicates the number of threads per inch.).

Typical applications: North America or special industrial equipment (such as vintage machinery, aviation components).

3. Strength grade

Hexagon socket head cap screws: Common grades include 4.8, 8.8, 10.9, and 12.9, with higher numbers indicating greater strength.

Grade 4.8: Ordinary mechanical structure, low cost.

Grade 8.8 and above: high-strength scenarios (such as car suspensions, bridge connections).

Hexagon socket screws: Their strength grade is generally lower than that of hexagon bolts, but their performance can be enhanced through the use of specific materials, such as alloy steel.

III. Comparison of application scenarios

Type Advantageous Scenario Disadvantageous Scenario

Hexagon socket head cap screws High-strength connection, ample space, cost-sensitive scenarios Scenarios with limited space or where screws need to be concealed

Hexagon socket screws: Scenarios with limited space, high appearance requirements, and precise adjustments; Scenarios with high torque demands and frequent disassembly leading to wear of the inner hole

IV. Key points of model selection

Space constraints:

In narrow environments, hexagon socket screws are preferred (such as inside equipment and pipeline connections).

When space is ample and high torque is required, choose external hexagonal screws (such as in building structures and heavy machinery).

Torque demand:

For high-strength connections (such as automotive suspensions), use Grade 8.8 or higher hexagon socket screws.

For precision adjustments (such as those on optical instruments), choose hexagonal socket screws and use a torque wrench to control the force.

Loosening prevention requirements:

For vibrating environments (such as engines), external hexagon screws with anti-loosening teeth or coated with threadlocker can be selected.

The anti-loose effect of hexagon socket screws can be enhanced by adding spring washers or using nylon lock nuts.

Material matching:

For humid environments (such as ships), stainless steel (such as 316) or galvanized screws are recommended.

Select heat-resistant alloy screws for high-temperature environments (such as engines).

V. Typical Cases

Automotive industry:

Mercedes-Benz cars commonly use M4-M12 hexagon socket screws to fix the chassis and engine components. It is necessary to select the model according to the specification table and control the torque.

Electronic devices:

The internal components of the mobile phone use M1.4-M2 hexagon socket screws to secure the circuit board, ensuring miniaturization and anti-loosening.

Furniture assembly:

IKEA furniture uses pan-head hexagon socket screws to connect wooden boards, balancing strength and aesthetics.