Three characteristics determine a screw's suitability for fence building: the screw's thread pattern, the screw's size and the screw's resistance to corrosion. Finding screws that match the requirements of a specific fencing project requires the builder to find screws that are long enough to penetrate through the fence's boards and into the fence's rails, but not so long that they protrude from the rail's rear. Understanding the desired characteristics of wood screws allows the outdoor builder to find the right fastener for a specific fencing project.
Wood Screw Threads
Wood screws for fencing applications must have a sharp point and woodcutting threads. The type of wood screws used on a wooden fence rail are often called "deck" screws. The woodcutting threads of a fence or deck begin at the screws tip and extend nearly all the way the screw's head. On the other hand, the threads of general-purpose wood screws often lead a smooth shank past the screw shaft's halfway point. Although preferable for fine woodworking, general-purpose wood screws are less effective for fencing applications than deck screws.
The proper screw size for a particular fence rail depends upon the width of the rail and thickness of the fence board. To effectively attach a board to a rail, the screw must run through the fence board and approximately halfway into the rail. The width of a standard fence rail is 1-1/2-inches, and the thickness of a standard fence board is approximately 5/8-inch to 3/4-inch. For most applications, fence screw length falls between 1-1/2-inches and 2-inches.
Outdoor Screws-Corrosion Resistance
The most important feature of an outdoor screw, such as a fence or deck screw, is resistance to corrosion. In general, there are two methods of providing a screw with resistance to corrosion: manufacturing the entire screw of a rust-resistant metal alloy or coating the screw's surface with rust-inhibiting coatings. Stainless steel is the most common rust-resistant alloy. However, stainless steel screws are often prohibitively expensive. Alternatively, manufacturers apply thin layers of rust-resistant alloys, such as zinc, to a steel fastener's surface. Coated fasteners are called "galvanized" screws. Although less expensive than stainless steel, galvanised fasteners generally have a shorter lifespan.
Although cross-shaped, Phillips-drive screws remain the standard for fence rail installations, manufacturers offer several types of speciality screws designed to facilitate easier and faster screw-driving. Square-drive and star-drive screws are a couple of the most common alternative screw-driving systems. As suggested by their names, the driver slot on a square drive screw's head is square-shaped, and the driver slot on a star-drive screw is star-shaped. These alternative slot shapes increase the bit's grip on the screw, improve torque and driving power and reduce stripping.