Understanding Wood Screw Types And Sizes: A Comprehensive Guide

Wood screws are designed to connect wooden pieces together. They feature coarse threads to grip the wood securely and a pointed tip to efficiently penetrate the wood surface. There are many types of wood screws available, including flat head, oval head, round head, pan head, trim head, truss head, and washer head. The size of the screw is indicated by a number, with #6, #8, and #10 being the most common. The length of the screw is also important, and it should be chosen based on the thickness of the wood and the load it will need to support.

Characteristics of Wood Screw Types and Sizes

Screw head types: flat, oval, round, pan, trim, truss, washer

Screw head types are either countersunk or non-countersunk. Non-countersunk heads are fully exposed and include binding, button, cheese, fillister, flange, hex, pan, round, socket, low socket, square, and truss. Countersunk designs, on the other hand, include flat, oval, and bugle heads. Flat and oval heads require a countersunk hole unless the material is very soft. The benefit of these designs is that little to no part of the head protrudes beyond the surface of the material.

Flat-head screws are available in a range of materials and can be used for a variety of applications. For example, flat-head wood screws are available in steel, zinc-plated steel, and tan, green, and gold exterior wood deck screws. Flat-head screws are also available as self-drilling sheet metal screws and self-tapping screws with wings.

Oval-head screws have a 90-degree countersunk angle and are designed for countersunk installation. The convex portion of the screw sits above the work surface. They are available in machine thread and self-tapping thread types. Machine thread screws are used in a tapped hole or with a locking/non-locking nut, while self-tapping threads are used with sheet metal or other materials.

Pan-head screws are non-countersunk and are available in a variety of materials, including steel, brass, and nickel-plated. They are used in a range of applications, such as wood screws, machine screws, and sheet metal screws.

Trim-head screws are not mentioned in the sources provided. However, trim screws are available, and they are likely non-countersunk, similar to pan-head screws.

Truss-head screws are non-countersunk and are available in a variety of materials, including steel, brass, and nickel-plated. They are used in applications such as wood screws, machine screws, and sheet metal screws.

Washer-head screws are available in round and hex designs. Round washer-head screws are traditional wood screws with a tight fit that yields maximum holding power. They are used in applications such as decking and construction. Hex washer-head screws require a wrench or socket for installation and removal.

Screw drive types: slotted, Phillips, square, hex, Torx

Slotted

Slotted screw drives, also known as flat-head screws, are perhaps the simplest type of screw drive. They have a single horizontal indentation (the slot) in the fastener head and are driven by a flat-bladed screwdriver. This was the first type of screw drive to be developed, and for centuries, it was the cheapest to make. The slotted screw is still found in existing products and installations, as well as in simple carpentry work and applications where minimal torque is needed. However, this design is not suitable for power tools as the power driver often cams out of the slot, causing damage to the screw and surrounding material.

Phillips

Phillips screw drives are characterised by a pointed tip, tapered flanks, and rounded corners. They are more stable than slotted screws, with four contact points. They are also more commonly used as they perform better with screwdrivers. Phillips screws are commonly used in DIY and construction projects, with many sizes of screwheads and drivers available. However, they strip easily and may cam-out or slip if driven at an angle.

Square

Square drive screws have a square-shaped socket and protrusion, with a slightly tapered tool and socket. This style is becoming increasingly popular as the tools used to drive them rarely slip out of place and are easier to insert. Square drive screws are most resistant to cam-outs or screwdriver slips, and the connections are tight. They are commonly used in woodworking and construction sites, as well as in projects that use composite materials or join angles. They come in two standard sizes: #2 and #3.

Hex

Hex head screws, like hex cap screws, require a wrench or socket for installation. They are designed to allow for greater torque. Hex screws are typically used in furniture installation and come with a matching-sized Allen wrench.

Torx

Torx screw drives, also known as star drives, have a six-pointed star shape. This entirely new design is gaining in popularity due to its ability to prevent cam-out. Torx screw drives are often used in the construction and manufacturing of electronic products. They are also used for high-torque applications.

Screw materials: brass, bronze, aluminium, steel, stainless steel

Brass, bronze, aluminium, steel, and stainless steel are all common materials used for wood screws. Each material has its own unique properties and is suitable for different applications.

Brass screws are traditional and have a yellow gold patina when new or polished. Over time, if left to age, brass will develop a yellow-hued brown tone, making it a good choice for antique brass hardware. Brass is also resistant to rust and corrosion when used with oak timber.

Bronze screws, specifically silicon bronze, are often used in boat building due to their corrosion-resistant properties. They are also available in a variety of head and drive types, including countersunk (CSK) flat and oval heads, round heads, slotted drive, frearson (R&P) drive, and square drive.

Aluminium screws are not mentioned in detail in my sources, but as a lightweight and malleable metal, it is likely that aluminium screws are used where weight and flexibility are important factors.

Steel screws are the most popular and commonly used type of wood screw. They are strong, versatile, and can be used without pre-drilled pilot holes in most wooden materials. Steel screws are available in a wide variety, including zinc-plated and hardened steel for enhanced durability and corrosion resistance.

Stainless steel screws offer good corrosion resistance and are commonly used in areas exposed to moisture. They are suitable for a range of wood materials and can be fitted with different head types depending on the desired finish.

Screw sizing: length, diameter, gauge

The sizing of a wood screw is important to ensure a secure connection between wooden materials. The length, diameter, and gauge of a screw are key factors in determining its suitability for a particular project.

Length

The length of a wood screw should be chosen based on the thickness of the materials being joined and the specific requirements of the joint. As a general rule, the screw should penetrate at least half the thickness of the bottom material and be long enough to securely fasten the two boards together without any protrusion. For standard wood screws, a length of three or four inches is typical, but they can range from 3/8 inch to six inches or more, depending on the type.

Diameter

The diameter of a wood screw refers to the width of the screw and is an important consideration when selecting the appropriate screw for a project. The diameter should be proportional to the width of the wooden material being used. A screw with a larger diameter will provide more strength and holding power, while a smaller diameter may be suitable for fine woodworking or light-duty applications.

Gauge

The gauge of a wood screw is indicated by a number, with the most common sizes being #6, #8, and #10. The number corresponds to the thickness of the screw, with larger numbers indicating a greater thickness. For example, a #6 screw is suitable for small crafts and light-duty applications, while a #10 screw is designed for heavy-duty construction and outdoor projects.

Screw use cases: small crafts, furniture, construction, heavy-duty, decorative

Wood screws are used in a wide range of applications, from small crafts to heavy-duty construction. Here are some common use cases for wood screws:

Small Crafts

Small wood screws such as a #4 or #6 are perfect for light-duty tasks such as small crafts, jewellery boxes, hinges, children's furniture, and toys. These screws typically range from 3/8 inch to 1 1/2 inches in length.

Furniture

Wood screws are commonly used in furniture construction and assembly. They are ideal for quickly building jigs, clamping forms, and joining cabinet and furniture parts. A #6 or #8 screw is a good choice for general furniture assembly, while a #10 screw is more suitable for heavy-duty furniture.

Construction

Wood screws are essential in construction projects, including general carpentry, deck construction, and cabinetmaking. A #10 screw is a good all-purpose option for general construction, while a #12 or #14 screw is designed for heavy-duty construction tasks.

Heavy-Duty

Wood screws can also be used for heavy-duty applications such as structural framing and hanging solid-core doors. For such tasks, a #12 or larger screw is recommended to provide the necessary strength and holding power.

Decorative

In addition to their functional purposes, wood screws can also be used decoratively. For example, brass screws can add a nice touch to a walnut cabinet or a mahogany jewellery box. There are also decorative domed or button plugs and screw covers available to enhance the appearance of fasteners.

Frequently asked questions