What are Lag Bolts? FAQs and More

What are Lag Bolts? FAQs and More

Fasteners are essential components in construction and DIY projects, playing a crucial role in ensuring structural integrity and durability. Among the various types of fasteners, lag bolts are particularly notable for their strength and reliability. This guide will explore what lag bolts are, their uses, and how to effectively work with them.

Are They Lag Bolts or Lag Screws?

Lag bolts, also called lag screws, are large, sturdy fasteners commonly used in wood construction. They are mostly commonly found with hexagonal heads and coarse threading - similar to bolts, but feature a sharp point - like screws. These two features create ambiguity between a bolt and a screw, which causes confusion. Still, they provide a strong grip in wood and other materials and unlike other bolts, lag bolts do not require a nut for fastening, making them unique and highly efficient in certain applications. For more information on the ambiguity between a lag bolt and a lag screw, check out our guide here.

What are Lag Bolts Used For?

Common uses of lag bolts are:

  • Construction: Lag bolts are ideal for securing heavy lumber and creating strong joints in construction projects.
  • DIY Projects: Home improvement enthusiasts use lag bolts to hang heavy items like shelves and to build structures such as decks and pergolas.
  • Industrial and Commercial: These bolts are used in industrial settings to secure machinery and in commercial applications where strong, reliable fasteners are needed.

What is the Difference Between a Lag Bolt and Other Bolts?

Lag bolts are excellent for heavy-duty wood applications where a strong, secure hold is needed. They are distinguished by their coarse threads and hex heads, designed for use with a wrench or socket. For projects involving metal or requiring fine-threaded fasteners, other types of bolts like machine bolts are more appropriate.

Other bolts can vary in strength and load-bearing capacity vary based on the bolt type and material. Machine bolts, for example, are used in metal-to-metal applications where high tensile strength is required.

Common Lag Bolt Materials and Sizes

Lag bolts come in various materials and sizes to suit different applications:

  • Materials: Common materials include galvanized steel, which provides some corrosion resistance and durability, and different grades of stainless steel (we offer 304 and 316 stainless steel), which provide even greater corrosion resistance for more extreme environments.
  • Sizes: Lag bolts vary in diameter, length, and thread pitch. Choosing the right size depends on the specific requirements of your project.

Understanding these specifications ensures that you select the appropriate lag bolt for your needs.

Do You Pre-Drill Lag Bolts?

The short answer is: sometimes, yes. In general, it's recommended to pre-drill pilot holes for lag bolts or lag screws; however, because lag bolts feature a pointed tip that can self-tap, you might not always need to pre-drill pilot holes. But as we stated, pre-drilling can reduce the risk of splitting wood - especially in hard wood or near the edges of boards, it can increase strength and ensure the accuracy of the bolt placement.

How to Install Lag Bolts

  1. Gather Tools: You'll need a drill, the appropriate drill bit for pilot holes, a wrench or socket set, and the lag bolts.
  2. Drill Pilot Holes: Pilot holes help prevent the wood from splitting and make it easier to drive the bolt in. Choose a drill bit slightly smaller than the lag bolt's diameter.
    1. A common guideline is to use a drill bit that is about 75% of the lag bolt's diameter. For example, if you are using a 3/8-inch lag bolt, a 9/32-inch drill bit would be appropriate.
  3. Insert and Tighten: Place the lag bolt in the pilot hole and use a wrench or socket set to tighten it. Ensure it is securely fastened but do  not overtighten, as this can strip the threads or damage the wood.

Safety Considerations

When working with lag bolts, safety is paramount:

  • Always choose the correct size and type of lag bolt for your project to ensure structural integrity.
  • Wear appropriate safety gear, such as gloves and eye protection, when drilling and installing lag bolts.
  • Avoid common mistakes like overtightening, which can strip the bolt or damage the material.

Purchasing Lag Bolts

When buying lag bolts, consider the following tips:

  • Select Quality Materials: Opt for high-quality materials that suit your specific application to ensure durability and strength.
  • Check for Certifications: Look for bolts that meet industry standards and certifications for safety and reliability.


Lag bolts are invaluable in construction and DIY projects due to their strength and versatility. By understanding their uses, installation methods, and safety considerations, you can confidently incorporate lag bolts into your projects. 

    Further Questions About Lag Bolts

    We offer a wide variety of fasteners and it can be daunting to decide which product best suits your needs. Our team of experts has a depth of knowledge in the fastener industry. If you have any additional questions be sure to reach out and we'll be glad to help.

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