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Lag Screws

Also known as lag bolts, lag screws are one of the toughest construction fasteners in the industry. The screws have coarse, sharp treading that only encompasses part of the bolt, which allows you to adjust it. Often made of steel, lag screws only come with hex heads due to the force needed to install them.Lag screws are often used in construction to fasten pieces of lumber together. A lag bolt provides a longer-lasting connection due to its length and is used for materials that may be subjected to a massive force or will bear a heavy load.



Lag screws can withstand significant stress without breaking or otherwise succumbing to damage. As a result, many manufacturing companies — as well as many construction companies — use lag screws to join heavy objects. Because they are longer and thicker than other screws, lag screws offer a higher level of performance. Their strong and durable properties keep them in place, even under the pressure of heavy objects.
In addition to their exceptional strength and durability, lag screws are long-lasting. A typical lag screw features a carbon steel core with a zinc exterior. Lag screws can last even longer if they are galvanized. Galvanizing protects the lag screw’s underlying steel core from rust and corrosion. Moisture and oxygen can’t easily penetrate galvanizing, so lag screws generally don’t rust or corrode with a galvanized finish. In regard to corrosion resistance lag screws can also be purchased in stainless steel. Stainless steel lags have superior corrosion resistance surpassing even a galvanized finish.

In addition stainless lags also boast a higher tensile strength than their steel counterpart. They can last for many years, all while offering a high level of stability and security to the objects on which they are used. Having said that, stainless lag screws will be more expensive. Anytime you are increasing durability and longevity to an item you can expect it will cost more. It just comes down to individual preference of the user and what they expect to get out of the product they are choosing for their project. Whether you are using steel zinc, steel galvanized, or stainless steel lags, you can expect a good deal of durability out of each fastener simply due to the design of the fastener. You simply add more anti-corrosive properties to the part the better the coating or material. This is also a consideration when you factor in the aesthetics of your project. Is it something that is going to be seen? Do you want the appearance to remain consistent over time? How will it look in 5 years? All things to be aware of.

Technical Data for Lag Screws

A full-bodied bolt with hex head, spaced threads and a gimlet point. Applications/ Advantages- Steel, Electro-plated Zinc: For use in wood in non-corrosive environments. Steel, Hot-Dip Galvanized: For use in corrosive environments. Stainless: Has superior corrosion resistance to galvanized steel bolts. Material Steel: AISI 1006 – 1022 or equivalent steel. Stainless: 18-8 stainless. Heat Treatment Stainless: The austenitic alloys develop their strength through work hardening during the fastener manufacturing process, as seen from the hardness properties below. The only heat treatment normally available on austenitic stainless alloys is annealing, which is done at approximately 1900°F to a dead soft condition and is not normally thermally reversible. Hardness Steel: Rockwell B70 – B100. Stainless: 1/4 through 1/2 in. diameter– Rockwell B95 – C32. Tensile Strength Steel: 60,000 psi. minimum Stainless: 100,000 – 125,000 psi. (approximate) Minimum Thread Length The minimum length of thread shall be equal to 1/2 the nominal screw length plus 0.50 in., or 5.00 in., whichever is shorter. Screws too short for this formula shall be threaded as close to the head as practicable.


Lag installation

To install a lag screw, align the materials you want to attach and use a clamp to hold them in place. If you have a team, someone can help you hold the wood in place. Use a bit to drill a pilot hole for the lag screw. You must create a preexisting opening that is slightly smaller than the bolt before installing the lag screw. Ensure that the hole is deep enough for the entire screw. Once you’ve fastened the bolt, tighten it with a power drill.
In addition to standard lag screws described above, there has been a new category of lags introduced in recent years typically referred to as “construction lags”. These fasteners offer some pretty amazing benefits over standard lag screws. It could possibly even be said these high strength construction lags are beginning to displace traditional lag screws as the fastener of choice for structural applications. Here are some things to consider when comparing the two. Structural screws (also called “construction” screws) are stronger than lags and make longer-lasting connections. You can just zip them in with any 18-volt drill (no pilot hole required). The labor difference is so huge that by the time you finish drilling pilot holes and ratcheting in just a few lags, you could have finished the whole job with structural screws and be on to the next thing.

Structural fasteners are made from stronger steel and are heat-treated for maximum strength. So even though they look less “beefy,” they’re actually one-to-one replacements for their fatter cousins. Some brands have a modified drill bit embedded into the screw point, so the screw literally removes wood as it spins. A few brands have rippled screw threads near the tip that saw a path for the remaining screw threads.

Structural screws also feature Torx (six contact points) or Spider (eight contact points) drive heads in addition to traditional hex-head styles.

The additional contact points spread the driving torque and prevent the kind of “cam-out” you get with Phillips or square-head drive screws. The straight-sided Torx and Spider bits also hold the screw in place so you can “aim” and drill with one hand. You can’t do that with a Phillips head or a hex-head lag. In many ways these construction lags are a game changer. The six lobe drive style that reduces cam-out , the larger surface area of the head eliminating the need for flat washers, the drill tips that eliminate the need for pre drilling, the high corrosion resistant surface treatment, and drill flute threads for ease of driving make these “construction lags” superior in many ways to standard lag screws.