The American Wood Council offers a Connection Calculator that determines connector capacity. Be sure to check it out along with this guide to find out how to choose the right wood screw length for your upcoming carpentry projects.
Screw Categories
There are two main types of screws for fastening wood out there. Utility screws (also known as deck screws) and steel / stainless steel screws. A utility screw is a workhorse; it’s used for framing and outdoor carpentry, coming in a range of materials, including corrosion-resistant metals. They work great with chemical-treated wood and are sold by length.
On the other hand, steel and stainless steel wood screws are used for more precision woodworking projects including indoor furniture. They have a thicker body and are identified by length and gauge (thickness). Larger gauges are thicker, smaller gauges are thinner.
Basics
The main goal when choosing the right wood screw is to use one that is long enough and stout enough to secure the boards together efficiently without splitting the wood or poking through the other side.
Pilot Holes
First, drilling a pilot hole with a countersink bit is the ideal scenario when working with hardwoods. Softwoods, on the other hand, probably do better without a pilot hole, as the screw gets its holding power via the wood fibers. Softwoods are less prone to splitting, so letting the screw grip the wood without a pilot hole will increase the screw’s holding strength.
Lateral Pressure vs. Withdrawal Pressure
The ultimate purpose of the piece you are constructing will determine the type of wood screw to use. If the piece will be subject to lateral pressure (pushing down or against), it is advisable to use a thicker screw.
If the piece is subject to withdrawal pressure (pulling apart), then you will want to make sure that the screw is long enough to withstand those forces. In this case, 1-1½ inches of screw thread should go into the receiving end. Obviously, avoid poking through to the other side of the board while doing so. If this is the case, then use a shorter screw but compensate by using more of them.
Grain Orientation
As a general rule, attaching two boards across the grain requires a shorter screw than when inserting into end grain, which requires at least two inches of screw thread into the board.
General Tips
- For a sheer strength piece, use a ¼-inch lag screw
- Use #8 diameter utility or deck screw for most tasks
- Use a 1¼-inch screw for basic tasks such as attaching ¾-inch boards across the grain
- Have on hand some 2½-inch utility screws for using in end grain
- Use a 3-inch screw for 2x boards into end grain, for a stronger connection
Hopefully, now you know how to choose wood screw length for your next woodworking project. At Fasteners, Inc. we are ready to help determine what wood screw you need and offer a wide assortment of fasteners for every project.