Lag screws for wood, also known as lag bolts, are one of the most sturdy and robust fasteners available for use in carpentry applications. They are much larger in diameter and length than a standard screw and are designed for heavy loads. They have a more aggressive thread profile and gimlet point that are ideally suited for forming strong clamping forces in wood to help prevent loosening or failure. Lag screws are available in a variety of materials and finishes for different uses, but the most common are either zinc plated or hot dip galvanized to offer superior corrosion resistance in harsh environments such as coastal areas, in addition to being suitable for pressure preservative treated lumber.
All screws and bolts are broadly categorized by their strengths, material and head shapes. Lag screws are some of the strongest and largest of all fasteners available, but they still come in a large variety of finish, size, material and head shape. To properly install a lag screw, the first step is to make sure that the materials you are fastening together are aligned correctly. This can be done by clamping the materials or by using another person to help you maintain a level of accuracy that ensures the lag bolt will be securely fastened.
Next, a pilot hole should be drilled into the materials through which the lag screw will pass. It is important that this hole is smaller in diameter than the screw, but should be deep enough to ensure that the lag bolt will have a good grip on the materials. Finally, the lag bolt can be installed through this hole and tightened as desired.
While lag screws for wood are very durable, there are new high-strength structural screws that are beginning to displace traditional lags in some construction projects. These high-strength construction screws have a more streamlined design and require less effort to drive, which can dramatically reduce labor costs for the project.
Whether you are building a timber frame home or simply attaching some logs to the main beam, the choice of fastener will greatly influence how long your project will last and the overall strength of the structure. Lag screws are a great choice for any application that requires heavy-duty fasteners, but there are new products on the market that can outperform even the strongest lags when it comes to strength and longevity.
SPAX PowerLags are made from high-quality steel and offer superior corrosion resistance to conventional lags. They are available in a wide range of sizes and are rated for use in all kinds of applications from timber frame construction to log home building. Unlike traditional lags, PowerLags do not need to be pre-drilled and can be driven into most any type of wood with an ordinary drill. This dramatically reduces labor costs on any construction or woodworking project and offers a better finished result with less time and effort spent driving screws and sanding.