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Lag Screw Vs Lag Bolt : Choose The Right Fastener

Fasteners have a wide range of applications in different industries. While some people say they use screws, others may say they must work mainly with bolts. For regular people, confusion arises with these two terms. Among these, the most used fasteners are lag screws and lag bolts.

Are these two technically different in structure and have other purposes? Here, we have tried to give you details to understand the difference between lag screws and bolts and how these two can be used in place of each other when needed.

What is a Lag Screw?

A lag screw is a screw with a hexagonal head that is often used to compress and join fracture fragments of different materials like large timber, wood, metal, etc. The lag screws are specially designed to bear the extreme load of joining these heavier materials and are some of the sturdiest fasteners used in the industrial sector.

The lag screws were initially used to join barrel staves or lags. Hence, these initially became known as lag screws with time. Mostly, the lag screws are made with stainless steel, zinc steel alloy, hot dip galvanized material, etc.

How to Install the Lag Screws?

The installation of the lag screw is as follows-

  • First, you want to join the screw with clamps along with the pieces.
  • Next, you must drill a hole of the same diameter as the screw shit in the material.
  • Then you must use the gimmel point to pull the screw inside the hole and fix the joints.
  • If you use lag screws with hex heads, you must use a driver bit and a power drill to drill the screw in its place.

How to Use a Lag Screw?

Lag screws are primarily used to join large pieces of timber together. Since these screws are very strong, they can hold up pieces and their extreme weight very well. Hence, the screws are used in construction sites, making ships or wooden items, etc. Lag screws are also used in making boats, submarines, and underwater structures as well/

Lag Screw Vs Lag Bolt

Well, lag bolts are specially designed threaded bolts with square or hex heads. The lag scenes are generally ¼ inch thick to ensure these can be durable enough to bear the load. In reality, the lag bolts and lag screws are the same. In other words, one item is referred with the name lag screws and lag bolts,

If you check out the structures of screws and bolts, you will find that bolt bolts come with a threaded machine line and can be easily fastened. On the other hand, you need to cut threads in the material and turn the screws to fit them in the hole.

Now, the word “lag” is attached to the larger items; most lag bolts are one inch long with a thickness of ¼ inch or more. In short, these are bigger than any other bolts; hence, these are referred to as lag bolts or screws. So, if you find someone who refers to lag bolts and another who talks about lag screws, both are technically talking about the same item.

What Are The Various Types Of Lag Bolts?

Here are the common types of lag bolts-

  • Silicon bronze lag bolts : are made with copper alloy and are commonly used in wooden boats. Due to the presence of copper, the boats can handle water and related corrosion better. Most silicon bronze lag bolts have a hex head and are six inches long. Such bolts are also used for high-heat environments or in places with extreme marine conditions.
  • Hot dipped galvanized lag bolts : The stainless steel made bolts are galvanized and come with galvanized butts. The molten Zinc creates a bonded alloy coating on the screws. The bolts also have a larger threading design to ensure the galvanized coating is not damaged during installation. These are incredibly corrosion-resistant and can be easily used in coastal areas also.
  • Zinc-plated lag bolts : The zinc-plated lag bolts are made with stainless steel and a fine coating of Zinc. It makes them rust-resistant and can be used in regular work. It is most common for case-hardened fastening works. You can find the bolts in different sizes. But, the zinc coating is not powerful enough, and these bolts are not recommended for extreme conditions.
  • Stainless steel 18-8 lag bolts : These are made with 304 or 305-grade stainless steel and are highly corrosion-resistant. Hence, these bolts are mainly used for exterior works or marine application projects. The screws are a size of 6 inches with a thickness of 3/8 inch. On top of that, lag bolts also come with coarse thread with a threading pattern. Most stainless steel screens come with a hex head for convenience. Another version is made with 316-stainless steel with the highest corrosion resistance power and is only used in extreme saltwater conditions.


The lag bolts or lag screws are technically the same item. These are stronger and larger screws that combine large timber or steel pieces. These screws also do not require pre-drilling and last for a long time.

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