Classification and application of screws

Screws are commonly used fasteners in mechanical connections, which fix two or more components together by rotation. Its classification methods are diverse, and can be divided according to dimensions such as head shape, driving method, thread type, material, and purpose. The following are detailed classifications and corresponding uses, combined with practical scenarios and purchasing suggestions:

1、 Classified by head shape: determines installation method and force characteristics

The shape of the head directly affects the installation tool and applicable scenarios of the screw, and the common types are as follows:

1. Flat Head Screw

Features: The head is flat, the top is flat, and the edges are 90 ° right angles or conical (countersunk design).

Purpose:

Scenarios that require a flat surface (such as furniture installation, fixing electrical enclosures) should have screw heads that do not protrude after installation.

Countersunk screws (conical) can be embedded in pre drilled holes, flush with the material surface, and are commonly used for woodworking and metal plate connections.

Example: Fixing wardrobe backboards and installing switch panels.

2. Round Head Screw

Features: The head is hemispherical in shape, with a smooth surface and rounded edges.

Purpose:

For decorative scenes such as toys and handicrafts, round heads can reduce the risk of scratches.

Suitable for soft materials such as plastic and wood, the round head can disperse pressure and avoid material cracking.

Example: Children's toy assembly, wooden frame fixation.

3. Pan Head Screw

Features: The head is in the shape of a flat disc, with a height between flat head and round head, and has a cross groove or a straight groove at the top.

Purpose:

Universal screws, suitable for connecting most metal and plastic components (such as electronic products and mechanical equipment).

The disc head design provides a larger contact area and enhances fixation stability.

Example: Computer case assembly, household appliance shell fixation.

4. Hex Head Screw

Features: The head is a regular hexagon and needs to be installed with a wrench or socket tool.

Purpose:

In scenarios that require high torque, such as building structures and car engines, the hexagonal head can withstand greater tightening force.

Commonly used in mechanical maintenance and pipeline connections, it has a better anti loosening effect than cross slot screws.

Example: Fixed bicycle wheel hub, water pipe joint connection.

5. Combination Head Screw

Features: The head combines two shapes (such as hexagonal and countersunk) to meet the requirements of installation tools and surface flatness.

Purpose:

Special scenarios (such as parts that require pre tightening with a wrench and adjustment with a screwdriver).

Commonly found in industrial equipment and precision instruments.

2、 Classified by driving method: determines installation tools and anti loosening performance

The driving method refers to the groove design of the screw head, which directly affects the installation efficiency and anti loosening ability:

1. Slotted Screw

Features: There is a straight groove on the head, which can be installed with a straight screwdriver.

Purpose:

Traditional design has low cost, but is prone to slipping (especially when the space is narrow).

Suitable for low torque scenarios (such as wooden furniture, simple appliances).

Avoid pitfalls: Avoid using in a vibrating environment as it may become loose.

2. Phillips Head Screw

Features: The head has a "+" - shaped groove, which can be installed with a cross screwdriver. The groove design can prevent slipping.

Purpose:

Strong universality, widely used in electronic products, home appliances, automobiles and other fields.

The depth and angle of the cross groove affect torque transmission, and corresponding screwdrivers need to be matched.

Advanced: Choose Pozidriv (PZ) groove (European standard), which is more slip resistant than regular cross grooves.

3. Hex Socket Screw

Features: The head has no exposed groove and requires an Allen Key for installation.

Purpose:

Scenarios that require high precision and anti loosening, such as mechanical assembly and bicycle components.

The head is low and can be embedded inside components, saving space.

Example: eyeglass frame fixation, drone component connection.

4. Torx Head Screw

Features: The head has a star shaped groove (similar to a plum blossom), which can be installed with a dedicated T-shaped screwdriver.

Purpose:

High torque transmission, better anti slip performance than cross grooves, commonly used in the automotive and aviation fields.

The groove design reduces tool wear and extends screw life.

Example: Car wheel hub cover, laptop shell.

5. Square Head Screw

Features: The head has a square groove, which can be installed with a square screwdriver or wrench.

Purpose:

Traditional industrial design has good anti loosening performance, but low tool versatility.

Commonly seen in old-fashioned furniture and railway equipment.

3、 Classification by thread type: determines applicable materials and connection strength

The thread is the core structure of a screw, which directly affects its ability to engage with the material

1. Machine Screw Thread

Features: The thread is fine and the pitch is small, and it needs to be used with nuts or pre drilled holes.

Purpose:

Metal component connections (such as steel plates and aluminum materials) require high precision and strength in scenarios.

Commonly found in mechanical equipment and electronic product casings.

Example: Computer motherboard fixation, metal bracket assembly.

2. Self Tapping Thread

Features: Sharp threads that can be directly drilled onto the material without the need for pre drilling.

Purpose:

Soft material connections (such as plastic, wood, thin metal) have high installation efficiency.

Commonly found in furniture, toys, and electrical enclosures.

Classification:

Sharp tail self tapping screw: suitable for thin plates (such as 0.5-2mm metal).

Flat tail self tapping screw: suitable for thick plates (such as metal above 2mm), pre drilled holes are required.

3. Wood Screw Thread

Characteristics: The thread is thick and deep, with a large pitch, and the head is usually round or flat.

Purpose:

Wooden material connections (such as furniture, doors and windows), with threads that can engage wood fibers to enhance fixation.

Pre drilling is required (with a diameter of approximately 70% -80% of the screw diameter) to prevent wood cracking.

Example: Bookshelf assembly, wooden staircase fixation.

4. Chipboard Screw Thread

Features: The thread is extremely thick, the pitch is large, the head is flat or countersunk, and the surface is often galvanized for rust prevention.

Purpose:

The connection of artificial boards such as density boards and particleboard, with coarse threads to prevent delamination of the boards.

Commonly used for custom furniture and cabinet installation.

4、 Classified by material: Determine applicable environment and durability

Screw materials directly affect their strength, corrosion resistance, and cost:

1. Carbon Steel Screw

Features: Low cost, high strength, but prone to rusting (requiring galvanizing or nickel plating for rust prevention).

Purpose:

Indoor dry environment (such as furniture, toys), short-term usage scenarios.

Avoid use in damp or corrosive environments (such as bathrooms, beaches).

2. Stainless Steel Screw

Characteristics: Strong corrosion resistance (especially 304 and 316 stainless steel), but slightly lower strength than carbon steel.

Purpose:

Wet environments (such as kitchens and bathrooms), outdoor scenes (such as railings and sunshades).

Food grade equipment (such as catering utensils, medical equipment).

3. Copper Screw

Features: Good conductivity, strong corrosion resistance, but low strength and high cost.

Purpose:

Electrical connections (such as wire connectors, grounding terminals), decorative scenes (such as antique restoration).

4. Plastic Screw

Features: Insulation, corrosion resistance, light weight, but low strength, prone to aging.

Purpose:

Internal fixation of electronic devices (such as battery compartments, circuit boards), and temporary assembly scenarios.

5、 Classified by purpose: directly corresponding to the usage scenario

According to functional requirements, screws can be further subdivided into:

1. Expansion Bolt

Features: Fixed in the wall through expansion pipes, requiring pre drilling.

Purpose:

Load bearing scenarios (such as hanging paintings, shelves, and air conditioning outdoor units) can withstand significant tensile forces.

Commonly found in hard materials such as concrete and brick walls.

2. Rivet

Features: Fixed in one go, requiring installation with a rivet gun, and dismantling requires destruction.

Purpose:

The connection (such as aircraft fuselage, car sheet metal) has good anti loosening performance.

Suitable for thin plates or scenarios where it is not possible to operate from the back.

3. Set Screw

Features: Headless, with one end threaded and the other end hexagonal or slotted.

Purpose:

Fix the relative position of two rotating components (such as gears and shaft sleeves) to prevent axial movement.

Commonly found in mechanical transmission systems.

4. Self Drilling Screw

Features: Drill tail design, allowing for direct drilling and tapping without the need for pre drilling.

Purpose:

Quick installation scenarios (such as metal roofs and color steel plate connections), with higher efficiency than self tapping screws.

6、 Selection suggestion: Match screw types according to the scene

Wooden furniture: Choose woodworking threads+round/flat head screws, paired with pre drilled holes.

Metal components: Select machine screw threads+hexagon head/hexagon socket screws to ensure strength.

Wet environment: Choose stainless steel or galvanized carbon steel screws, with rust prevention as a priority.

High vibration scenario: Choose plum blossom groove or hexagonal drive screw, with strong anti loosening performance.

Temporary fixation: Choose plastic screws or self tapping screws for easy disassembly.

summarize

The core classification of screws is "structure+material+function", remember the following mnemonic:

Head positioning tool, thread material selection, usage depends on the scene, anti loosening is the key

By matching installation requirements, material characteristics, and environmental conditions, suitable screws can be easily selected to ensure a stable and durable connection.