Types of screws

Screws are common fasteners that secure two or more objects together by rotating. They are widely used in various fields such as machinery, construction, electronics, and furniture. Based on dimensions such as head shape, slot type, usage, and material, screws can be categorized into multiple types. The following are common classifications and detailed descriptions:

1. Classification by Head Shape: The shape of the head directly affects the force distribution and installation scenarios of screws. Common types include:

Characteristics of Flat Head Screw: The head is flat, with a conical top, and it is flush with the surface of the material after installation.

Purpose: For scenarios requiring a smooth surface (such as furniture, electrical appliance casings), to avoid prominent scratches.

Example: Flat-head type of wood screws and self-tapping screws.

Round Head Screw features a hemispherical head that protrudes above the surface after installation.

Purpose: Scenarios where a certain protrusion height is required to increase friction (such as mechanical connections and toy assembly).

Example: machine screws, decorative screws.

Characteristics of Countersunk Head Screw: The head is conical at a 90-degree angle, allowing it to fully sink into the material after installation, resulting in a flat surface.

Purpose: For scenarios where high surface smoothness is required (such as metal sheets and glass installation).

Example: stainless steel countersunk head screws, cross recessed countersunk head self-tapping screws.

Hex Head Screw Features: The head is hexagonal, requiring the use of a wrench or socket tool for installation.

Purpose: Scenarios requiring high torque and high strength (such as building structures and automobile maintenance).

Example: Hexagonal bolt, hexagonal socket head cap screw (requires an Allen wrench).

Pan Head Screw Features: The head is dome-shaped, falling between the flat head and the round head, and protrudes slightly after installation.

Purpose: General scenarios, such as electronic equipment and small machinery assembly.

Example: Cross recessed pan head self-tapping screws, combination screws.

II. Classification by slot type: The slot type determines the driving method of the screw. Common types include:

Slotted head features a straight groove on the head, which can be driven with a straight screwdriver.

Advantages: simple and versatile, low cost.

Disadvantages: prone to slipping, low torque transmission efficiency.

Purpose: Traditional furniture, low-torque scenarios.

Characteristics of Phillips/Cross Recessed head: It features a cross-shaped groove on the head, which is driven by a Phillips screwdriver.

Advantages: Even torque transmission, less prone to slipping.

Purpose: Widely used in electronics, home appliances, automotive, and other fields.

Variant: PZ slot (Pozidriv, commonly used in Europe, compatible with Phillips screwdriver but more anti-slip).

Hex Socket features a hexagonal groove on the head, which is driven by an Allen wrench.

Advantages: Capable of withstanding high torque, with a low and compact head, suitable for precision assembly.

Purpose: Hidden connection for machinery, instruments, and furniture.

Examples: Hexagon socket head cap screws, hexagon socket countersunk head screws.

Characteristics of Torx/Star: The head features a star-shaped groove, which is driven using a Torx screwdriver.

Advantages: High torque transmission efficiency, almost no slipping, long service life.

Purpose: High-precision applications in automotive, electronics, aviation, and other fields.

Variant: Security-type Torx recess (requires specialized tool, tamper-proof).

Square Recessed features a square groove on the head, which is driven using a square-head screwdriver.

Advantages: Its anti-slip performance surpasses that of a straight slot, and it offers superior torque transmission.

Purpose: Traditional woodworking and construction fields.

III. Classification by Purpose: Based on application scenarios and functions, screws can be divided into the following types:

Wood screw features: deep thread, large spacing, sharp tip, no need for pre-drilling.

Purpose: Connection of wood and soft materials (such as plastic and fiberboard).

Example: Self-tapping wood screws, double-headed wood screws.

Self-tapping screw features a sharp thread that allows it to be directly screwed into metal or plastic without the need for pre-drilling.

Purpose: Rapid fixation of metal sheets and thin-walled materials (such as air conditioning installation, metal frames).

Variant: Self-drilling screw (with a drill bit tip, capable of drilling and tapping simultaneously).

Characteristics of Machine Screw: Small diameter, fine thread, requiring use with a nut or threaded hole.

Purpose: Precise connection of mechanical and electronic devices (such as circuit board fixation and instrument assembly).

Example: Cross recessed machine screws, hexagonal machine screws.

Expansion bolt features: It is fixed in the hole through an expansion sleeve, providing strong tensile strength.

Purpose: For securing hard materials such as concrete and brick walls (e.g., for ceiling fan and bracket installation).

Example: metal expansion screws, plastic expansion tubes.

Characteristics of Combination Screw: It features a washer or spring washer on the head to prevent loosening.

Purpose: Fixing in vibrating environments (such as motors, mechanical equipment).

Example: Cross recessed combination screws, hexagonal combination bolts.

Chipboard Screw Features: Thick and deep threads, sharp tip, suitable for chipboard and particle board.

Purpose: furniture assembly, panel connection.

4. The material of screws directly affects their strength, corrosion resistance, and applicable scenarios, depending on the classification of materials:

Characteristics of carbon steel screws: high strength, low cost, but prone to rust.

Purpose: Indoor dry environment (such as furniture, toys).

Treatment: Galvanizing and blackening treatments can prevent rust.

Characteristics of stainless steel screws: strong corrosion resistance and moderate strength.

Purpose: Outdoor use, in humid environments (such as buildings, ships, and food equipment).

Grade: 304 (general purpose), 316 (seawater corrosion resistant).

Characteristics of copper screws: good conductivity, corrosion resistance, but low strength.

Purpose: Electronic and electrical fields (such as grounding screws).

Variants: Brass screws (more commonly used), copper screws (high conductivity).

Characteristics of aluminum alloy screws: lightweight, corrosion-resistant, but low in strength.

Purpose: Lightweight applications in aviation, sports equipment, and other demanding scenarios.

Characteristics of plastic screws: insulating, corrosion-resistant, but low in strength.

Purpose: Electronic devices, acid and alkaline environments (such as battery fixation, laboratory equipment).

5. Features of anti-theft screws for special purposes: The head design is unique (such as a five-pointed star or a torx security slot), requiring a special tool for disassembly.

Purpose: Public facilities, license plate fixation, and other tamper-proof scenarios.

Characteristics of high-temperature screws: Made of high-temperature resistant materials such as nickel-based alloys and ceramics.

Purpose: For use in high-temperature environments such as engines and boilers.

Characteristics of micro screws: with a diameter less than 1mm, used for precision instruments.

Purpose: assembly of glasses, watches, and electronic chips.

VI. How to choose screws?

According to the materials: use wood screws for wood, and self-tapping screws or machine screws for metal.

Based on the environment: choose stainless steel for humid environments, and carbon steel for dry environments.

Based on the force applied: hexagonal head for high torque, and hexagonal socket or torx for precision assembly.

Based on aesthetics: For surfaces that need to be flat, choose countersunk heads; for prominent decoration, choose round or disc heads.

Example scenario:

Install wooden bookshelf: wood screws (carbon steel, galvanized) + flat head.

Fixed metal air conditioning bracket: self-tapping screw (stainless steel) + hexagonal head.

Assembling electronic equipment: machine screws (copper) + Phillips head.

Summary: There is a wide variety of screws, and when selecting, it is necessary to comprehensively consider factors such as material, head shape, slot type, usage, and environmental conditions. Proper matching ensures a secure, durable, and aesthetically pleasing connection!