Lag Screws

Lag screws bring strong fastening power to wood-to-wood connections and projects that attach hardware to substantial wood framing. Often called lag bolts, these heavy-duty wood fasteners have coarse threads that grip the wood and a pointed tip that helps position the screw for installation. Unlike a standard through-bolt, a lag screw typically threads directly into wood rather than fastening with a nut on the opposite side. Many lag screws have a hex head that you can tighten with a socket or wrench, making them a practical option for jobs around the barn, workshop or property where the connection calls for this type of fastener. Choosing the right lag screw size starts with the thickness of the pieces you’re joining, the required thread penetration into the supporting wood and the demands on the connection. A longer or wider screw isn’t automatically the right pick: Screw diameter, length, spacing and distance from the wood’s edges all play a part in getting the job done right. Proper lag screw installation helps limit splitting and gives the threads a firm hold. Traditional lag screws generally need a pilot hole in the receiving wood, and the piece being attached may also need a clearance hole for the unthreaded shank. Follow the fastener manufacturer’s directions for drill bit size, hole depth and installation requirements, since wood density and screw dimensions affect the fit. A compatible washer beneath the head can help spread pressure across the surface where the connection design calls for one. Tighten the fastener until the joint is snug without crushing the wood or overtightening and stripping the hole. For outdoor lag screw applications, check that the fastener’s corrosion protection suits the weather exposure, any treated lumber and the attached hardware. Deck connections, structural framing and other load-bearing work need fasteners and installation details that meet the applicable plans and local building requirements. Before starting your next farm repair or wood construction project, check those details so your lag screws match the job, not just the hole.