Screws are a very common type of fastener industry. They seem simple but come in many varieties. They play a key role in different application scenarios. As a factory professional who has been dealing with screws for more than ten years, Today, I will take you to have a deeper understanding of the classification and use of these key roles that connect everything.

Classification By Head Shape:

The head of the screw is the first step in screw forming, which also determines its final appearance and function:

1. Round Head Screw:

 The classic arc top and slightly flat bottom. The head will slightly protrude from the surface after installation. Suitable for occasions where appearance is not required and strength is prioritized, such as some internal structure connections.

2. Flat Head/Countersunk Head Screw:

The top is flat and the bottom is conical. It needs to be used with countersinks. After tightening, the head is flush with the surface of the material or slightly lower than the surface, providing a smooth appearance. It is commonly used in furniture, door and window frame installation.

3. Oval Head/Semi-Countersunk Screw:

Combining the beauty of the round head with the characteristics of the flat head being partially sunken, the bottom is conical and the top is arched. After screwing in, the head is slightly raised but more delicate, and is mostly used for decorative metal parts or electrical panels.

4. Hex Head Screw:

The head is a hexagonal column. It provides super strong torque resistance and is often tightened with a wrench or socket. It can withstand a large tightening torque and is a frequent customer for heavy machinery, steel structures, and automobile repairs.

5. Hex Washer Head Screw:

 A round or serrated flange gasket is integrated at the bottom of the hexagonal head. The flange increases the pressure-bearing surface, disperses the load, and helps prevent loosening and seal. It is often used to connect softer materials (such as wood and composite materials) or occasions where sealing gasket functions are required (such as some sheet metal connections).

6. Pan Head Screw:

The top is a wide and flat arc and the bottom is straight. It provides a larger pressure-bearing area than the round head, the head is obviously protruding, and it is easy for tools to contact. It is commonly used in the assembly of electrical and mechanical equipment housings.

7. Wafer Head Screw:

Wafer head screw its head is low, with a large pressure-bearing surface and slightly convex. It is used in places where a flat appearance is required but the space or material limit prevents countersunk heads (thin plates, interior decoration, electrical appliances).

8. Trim Head Screw:

This screw has a very small head, shallow sinking, invisible and beautiful characteristics. It is used in high-end woodworking, fine furniture, cabinet finishes and other installations with aesthetic requirements.

9. Bugle Head Screw:

The bottom of the screw head is designed with a flared mouth, and its core function is to prevent the tearing of the gypsum board paper surface. Its application scenario is gypsum board fixing

Classification By Raw  Material：

The strength of screws is determined by their materials. Different materials directly affect performance, service life and cost

1.Carbon Steel Screw:

The most common type, economical and moderately strong. The general material is C1022, which needs to be matched with surface treatment to improve its anti-rust ability. It is widely used in building frames, general wooden structures, and indoor and outdoor non-high-corrosion environments.

2.Stainless Steel Screw: 

Known for its excellent corrosion resistance, it is especially suitable for humid, outdoor or chemical environments. Common grades include 304 (general purpose) and 316 (stronger resistance to seawater and chemicals). Kitchens and bathrooms, ships, coastal buildings, and food processing equipment are its main application scenarios.

3.Brass Screw:

 It has good corrosion resistance and conductivity, beautiful appearance (golden yellow), and lower strength than steel. It is often used in decorative hardware, electronic grounding, special occasions requiring non-magnetic properties, and certain waterway applications, but attention should be paid to dezincification corrosion.

4.Alloy Steel Screw: 

The strength, hardness or toughness is improved by adding elements such as chromium, molybdenum and vanadium to carbon steel. Heat treatment (such as quenching and tempering) is often performed to achieve high strength grades (such as 8.8, 10.9, 12.9 bolts), which are used for critical structural connections that withstand high stress, automobile engines, and heavy machinery.

5.Aluminum Screws: 

Made of aluminum alloy (commonly known as 6061-T6). Its core advantage lies in its extreme lightness and good natural atmospheric corrosion resistance. It is usually silver-white in appearance or anodized into various colors, which is both beautiful and corrosion-resistant. It is mainly used in situations where weight is extremely sensitive or magnetic interference needs to be avoided.

Classification By Tail and Tapping Characteristics:

According to the design of the screw tail, screws are divided into two categories: self-drilling and self-tapping. The difference in the tail significantly affects the installation method:

1. Self-tapping screws:

 The tip is specially designed, such as a conical tip, a blunt tip with a groove, which can directly “cut” or “extrude” a matching thread in a softer material like plastic, thin metal, wood or a hole without pre-made threads. Mainly used in the assembly of furniture, thin metal plates, and plastics

2. Self-drilling screws: 

The tail has a sharp tip like a drill bit. The biggest advantage is that it can directly drill holes in thin steel plates, aluminum alloys and other materials and form threads simultaneously, in one step, eliminating the pre-drilling step and greatly improving efficiency. The drill tail has a variety of shapes to adapt to different materials and thicknesses. It is the main screw for steel structure installation, metal roofs, and ventilation duct construction.

Classification By Drive Mode:

Different drive types determine which tools are used to install or remove screws

1. Cross-slot screw (Phillips – PH): 

The most common type, cross-grooved with a Phillips head screwdriver or electric screw gun. Note that the bit is easy to “jump out” under high torque. It is highly versatile and can be found everywhere in home DIY and electrical appliance assembly.

2. Slotted screw : 

The oldest and simplest straight groove. The tool is easy to obtain, but the bit is very easy to slip and damage the notch or workpiece. Modern applications have decreased, and it is more common in old furniture or specific low-torque occasions.

3. Square head/Robertson screw: 

The head is a square pit. The bit is firmly embedded, can withstand high torque, and has an anti-slip design. It is very popular in North American wooden structures.

4. Hexagonal/Allen screw: 

The head is a cylindrical concave hexagonal hole. Use an L-shaped hexagonal wrench or hexagonal bit. The contact surface is large, and it can transmit extremely high torque. The head can be designed to be very small or sunk into the workpiece. It is widely used in furniture assembly, bicycles, and mechanical equipment.

5. Torx  head/star head screw: 

The head is a unique hexagonal star groove. It fits perfectly with the Torx bit, with the largest contact area, providing extremely high torque transmission capacity and anti-slip performance, which can effectively reduce the wear of the bit and the damage of the screw head. It is increasingly used in automobiles, electronic products, and industrial assembly that requires high reliability. The anti-tampering Torx (Security Torx/Torx TR) with a center column increases the difficulty of disassembly.

6. Composite groove screw: 

Common ones such as cross/slot (Pozidriv – PZ), add radial small ribs on the basis of the cross to reduce the cam effect, and the torsion capacity is better than the standard cross slot. It is very common in European woodworking and construction fields. There are also cross/square head designs to increase tool compatibility.

Classification By Use:

In order to meet different installation scenarios, various screw designs have emerged.

1. Wood Screws: 

A classic choice. Usually pointed (self-tapping), the shaft part is unthreaded (smooth rod), the thread is deep and sharp, and most of them are flat or round heads. The smooth rod section allows the upper part of the wood to shrink and expand freely without cracking, and is the core of furniture and wood structure connections.

2. Drywall Screws: 

Drywall Screws designed specifically for gypsum board. Fine-pointed self-tapping threads, the head is mostly a trumpet head or a countersunk head with a fine-tooth flange, and the material is mostly phosphating black or galvanized. The trumpet head can sink into the gypsum board without tearing the paper surface, and the fine thread ensures reliable engagement on the light steel keel. It is a special part for indoor partition wall and ceiling installation.

3. Roofing Screws:

 Expert in fixing metal roofs or tiles. Most of them are self-drilling designs (with drill tails) to deal with metal purlins. The head is oversized (usually a hexagonal flange head) and equipped with a special rubber or EPDM gasket to ensure a waterproof seal. The material is usually a highly weather-resistant galvanized steel or stainless steel.

4. Machine Screws: 

Used with prefabricated threaded holes (such as nuts, threaded sleeves, and screw holes on machined parts). The rod is fully threaded, the head has various shapes (round head, flat head, pan head, hexagonal head, etc.), and the tail is usually flat. With precise dimensions and clear strength grades (such as SAE or metric grades), it is the cornerstone of precision assembly inside mechanical equipment and electronic products.

5. Window Screws: 

Used to fix window frames (wood, PVC or metal). Usually flat or round head, self-tapping design. The key points are accurate length (to avoid penetrating the frame and damaging the seal) and corrosion resistance (stainless steel or high-quality coating) to ensure long-term stability and waterproofness.

6. Sheet Metal Screws: 

Specializes in thin metal sheet connections. Most of them are self-drilling with pointed heads or self-drilling with drill tails, with fine and sharp threads and strong penetration. Common pan heads, hexagonal flange heads or head types with washers provide sufficient pressure-bearing surfaces to prevent pulling through thin plates. They are the main force in the assembly of ventilation ducts, electrical boxes, and metal casings.

7. Studs: 

Both ends have threads, and the middle is threadless or partially threadless. One end is screwed into the substrate (such as the body), and the other end is used to screw nuts to fix other parts. They are indispensable when it is necessary to frequently disassemble connectors (such as automobile cylinder heads) or provide installation bases (such as wall-mounted pendants).

8. Anchors: 

Strictly speaking, they are not screws, but kits used to create fixing points on substrates such as concrete and brick walls. They usually include metal sleeves and matching bolts/screws. When the bolts are screwed in, the sleeves expand and lock the substrate hole wall, providing strong pull-out resistance. They are the key to mounting heavy objects on the wall (shelves, TVs, equipment).

9. Concrete Screws / Masonry Screws: 

Designed for attaching materials to hard and brittle substrates such as concrete, brick, and masonry blocks. Typically made from high-hardness steel (carbon steel or alloy steel), these screws require a pre-drilled hole of precise diameter and depth. They are used for securing door and window frames to concrete walls, installing electrical boxes and plumbing brackets to masonry walls, and connecting wood structures to concrete floors.

10. Coach Screws / Lag Screws: 

These are oversized wood screws. They have a large square (or hexagonal) head and require a wrench or socket to apply high torque. They are the preferred fastener for heavy wood structures and are used for wood-to-wood connections requiring extremely high strength, such as those for connecting log cabin framing, heavy wooden outdoor furniture (gazebos and benches), securing fence posts, large wooden playground equipment, and wooden bridge structures.

11. Chipboard Screws / Particle Board Screws:

 Experts in solving difficult furniture material joining problems. Wood-based artificial boards such as particleboard, medium-density fiberboard (MDF), and oriented strand board (OSB) have loose internal structures, poor nail holding power, and are prone to cracking at the edges.

Classification By Surface Treatment 

1. Phosphating Screw:

Soak the screws in a phosphate solution to produce a chemical reaction, forming a gray-black or gray insoluble phosphate crystal film on the surface. This film has general corrosion resistance, low cost, and mature technology. It is suitable for dry environments, such as the installation and fixation of indoor objects.

2. Galvanizing  Screw: 

(1) Electro-galvanizing (Zinc Plating): 

Using the principle of electrolysis, a thin layer of zinc (usually a few microns to more than ten microns) is evenly deposited on the surface of the screw. The color is silvery white and bright. Color passivation is often performed after plating to greatly improve corrosion resistance and increase aesthetics. Suitable for household appliances, electronic products, indoor furniture, automotive interior parts, general building hardware, and standard parts. 

(2) Hot-dip galvanizing ：

 Immerse the pickled screws in molten zinc solution (about 450°C). After removal, a thicker zinc-iron alloy layer and pure zinc layer are formed on the surface. The appearance is a distinctive silver-gray with zinc patterns and a rough surface. Suitable for heavy-duty outdoor structures such as power towers, highway guardrails, and large steel structures.

3. Dacromet Screw

A revolutionary “hydrogen embrittlement-free” coating. Ultra-fine zinc and aluminum flakes are suspended in a special water-based chromate solution, applied to the screws by dipping or spraying, and then cured at high temperature. The resulting coating is a matte silver-gray or silver-white, remarkably uniform. This screw is suitable for high-strength fasteners such as automotive engines and chassis (to avoid hydrogen embrittlement fracture), brake systems (for high-temperature resistance), and outdoor precision components (such as railway fasteners and signaling equipment). It can also replace some electroplated and hot-dip galvanizing applications where extremely high corrosion resistance is required and excessive thickness is not an issue.

4. Hot Ruspert Screw

Hot Ruspert Screw: This is a specialized self-drilling screw designed specifically for metal roofing applications in high-temperature environments. Its core feature is its high-temperature-resistant coating (such as a high-quality zinc-aluminum coating or a similar process like Hot Rust). This allows it to maintain excellent corrosion resistance even under continuous exposure to high temperatures (often exceeding 80°C or higher) caused by intense sunlight, preventing premature coating failure. Furthermore, its self-drilling design allows it to easily penetrate metal roof panels and underlying purlins. Its large-diameter flange and heat-resistant sealing gasket (typically EPDM or silicone) ensure a reliable waterproof seal despite thermal expansion and contraction. It is a key fastener for high-temperature metal roof installations in industrial plants, large warehouses, and other locations.

5. Color Coating Screw

The screw surface is electrostatically coated with a powder coating, then baked and cured, or painted. Available in a wide variety of colors (customizable in any RAL/Pantone color), it offers corrosion resistance, excellent insulation, and a decorative effect. Suitable for decorative fastening in visible areas, such as outdoor furniture, amusement rides, and door and window hardware.

6. Blackening/Black Oxide Screw:

The screws react in a high-temperature, strong alkaline solution (containing an oxidizing agent), forming a dense, magnetic film of ferroferric oxide (Fe₃O₄) on their surface. The color is deep black or bluish-black with a matte finish.

This is primarily used for indoor equipment requiring a black appearance and in dry environments, such as the interiors of some home appliances and office furniture hardware.

7. Nickel Plating Screw:

A layer of nickel is deposited on the screw surface through electroplating.

The resulting coating is more uniform, has no edge effects, offers high hardness, excellent wear and corrosion resistance, and adjustable phosphorus content.

This results in a high-end appearance, excellent wear and corrosion resistance (especially with electroless nickel), good conductivity, and a certain degree of lubricity (especially with electroless nickel), but at a higher cost. Used for decorative parts and high-end furniture hardware requiring excellent appearance and corrosion resistance.

8. Blueberry Teflon

A dense blue oxide film (Fe₃O₄) is formed on the screw surface through high temperatures (approximately 300°C) or chemical methods (alkaline solutions). The color is dark blue or blue-black with a unique metallic luster. It is primarily used in high-end knives, firearms, models, musical instrument accessories, and vintage-style hardware, where a unique appearance is paramount.

Conclusion：

The classification and analysis of screws goes far beyond this. Each small screw embodies a sophisticated design tailored to specific needs. Understanding their classification and characteristics is the basis for choosing the most appropriate connection solution and a key step in ensuring a strong and reliable project. If you want to learn more about screws, you can contact us at any time. Sinsunfastener is willing to provide you with valuable information.