Lag Screws

Lag Screws

Lag screws are the heavy hitters for wood-to-wood connections where you need real holding power. You’ll see them on deck ledgers, porch posts, pergolas, and other structural builds. They’re often called lag bolts on jobsites, even though they’re technically screws. The hex head makes them easy to drive with common tools, even in tight spots.

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Common Uses for Lag Screws

From framing repairs to new builds, lag screws are a go-to when a standard wood screw feels undersized. They’re commonly used to attach beams to posts, mount brackets and hardware, secure deck joists and ledgers, and fasten stair stringers. Because hex lag screws can be driven with a wrench or socket, they’re a solid pick when you need more torque than a driver bit can handle. Choose a corrosion-resistant finish for outdoor work, and size the shank to the load so the connection stays tight. Getting the right length matters too, since you want enough thread engagement without punching through the far side. Done right, they bring many benefits: fewer loose connections, cleaner installs, and less rework later. A washer under the head helps spread the load.

How to Install Lag Screws Properly

Start by laying out your hole locations and checking for obstructions. Bore a pilot hole so the threads bite without forcing the wood apart. For larger diameters, use a clearance hole in the top piece and a smaller pilot in the receiving member, then keep everything aligned so the joint pulls together evenly. Use a drill at a steady speed, keep the tool square, and drive until the head is snug and the joint closes. Stop once it’s seated; over-tightening can crush wood fibers and reduce grip. Add a washer when the head could sink into soft lumber. If you’re near an edge, increase the pilot size slightly so the fastener can work correctly without splitting. For outdoor builds, match the coating to treated lumber, too.

Wholesale Lag Screws for Contractors and Builders

If you’re buying for crews, standardizing fasteners keeps jobs moving and helps inspections go smoother. Fastener SuperStore supports box and case ordering so you can stock consistent sizes for recurring work, such as deck packages, timber features, and facility maintenance. That’s also helpful when you’re tracking specs across multiple sites and need the same head style and finish every time. Some projects mix substrates so that you might be quoting screws for concrete work as well. If that’s the case, you can also find a screw for concrete work in our anchor categories, including bulk concrete screws and the screws concrete finishes and cement masons need. If you landed here searching for concrete screws for sale, you’re not alone; our team can point you to the right product family fast.

Frequently Asked Questions:

What materials can lag screws be used with?

Lag screws are made for wood: dimensional lumber, timbers, and many engineered wood products. They can also fasten wood parts to brackets, straps, or plates, as long as the threads are biting into wood. When you’re going through metal, size the through-hole so the shank passes cleanly. 

What is the difference between a lag screw and a wood screw?

A lag screw is larger, has a hex head, and is intended for higher-load connections like ledgers, posts, and heavy hardware. A typical wood screw is smaller, often uses a Phillips or Torx drive, and is better for lighter-duty fastening, trim, and general carpentry.

What sizes do lag screws come in?

Lag screw sizes are listed by diameter and overall measurement, with options ranging from short fasteners for blocking and brackets to long fasteners for beams and posts. Your best choice depends on member thickness, required embedment, and the loads at the joint.

What tools do I need to install lag screws?

Plan on a socket or wrench to drive the hex head, plus bits to make a pilot hole and, when needed, a clearance hole. A ratchet, impact wrench, or power driver can work depending on fastener size and access. Washers help when the head could sink into soft lumber.

What is the minimum order size for wholesale lag screws?

Minimums depend on the exact item and packaging. Most wholesale quantities are sold by the box, with case options available for higher-volume needs. If you’re building a takeoff and want help matching counts to your job, customer service can recommend the best pack size.