What are lag screws? Leave a comment

A lag screw is a surgical screw that has no thread on the proximal part of the screw head. This enables the goal of interfragmentary compression.


A lag screw is a large, coarse thread screw with a hex head that is used to tighten or remove it. A conventional screw uses a screwdriver to tighten or loosen, while the lag screw uses a wrench. Similar to a bolt, the lag screw is used in situations where maximum strength and a clamping force are required. Projects like securing a deck to the wall or the foundation of a house usually require the use of screw mounting construction. Assembly gates, swing doors, and even garage door rails are typical overrun applications.


When attaching an object such as a wooden board to another wooden structure with an anchor screw, you must first drill a pilot hole through the two boards. The anchor screw can be screwed through the guide hole through the first and into the second board without dividing any of the boards. Trying to drive the anchor bolt through the first board without a pilot hole will usually result in a split or cracked board that must be replaced. It is recommended to use a washer under the head of the lag screw to prevent the head from being sucked into the wood over time.


One of the advantages of using a lag is that it can be tightened well beyond that of a standard screw. By placing a wrench on the hex head of the screw, enormous pressure can be exerted on the screw without damaging the screw head. The hexagonal head enables easy removal even after a long period of time. Using a wrench instead of a screwdriver also allows you to manipulate the screw in much tighter areas than can be done with a screwdriver.


The typical anchor bolt or screw is chrome-plated or shiny zinc-plated to prevent rust and corrosion from weakening or breaking the screw. Using pressure-treated lumber and a resilient lock, the average home deck can survive for years with very little maintenance. The great strength of a lag screw also makes the fastener a smart choice when installing gate hinges on a wooden post. The weight and movement of a heavy iron gate will not easily solve the delay. The gate will likely stay tight for years without having to retighten the hinge screws.

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