The Difference Between Lag Bolts and Carriage Bolts

Bolts are a mechanical fastener that feature an external male thread, capable of mating with a matching preformed internal thread to secure and assemble two or more parts together. As one of the most common fasteners used for assemblies ranging from DIY home projects to advanced aircraft construction, there are many types available that one may procure for their given requirements. The carriage bolt and lag bolt are two common types, each of which present their own unique characteristics and advantages. To help you best understand the difference between carriage bolts and lag bolts, we will provide a brief overview of each in regard to how they are designed, how they serve assemblies, and more.

The carriage bolt is a fastener type that may be distinguishable by its shallow mushroom head and squared shank underneath. Due to the squared shape placed under the head of the bolt, carriage bolts are capable of self-locking as a lockbolt when the assembly features a square hole. Commonly used to secure metals to metals or metals to wood, such bolts only require a single spanner or wrench for installation from one side. Carriage bolts are not commonly fully threaded, instead featuring a section of the length that is smooth. Carriage bolts also have a flat end on the opposite side of the head, requiring a washer and nut for securing the assembly. For their applications, carriage bolts may be used for locks and hinges, wood construction, dock construction, and more.

While the carriage bolt is fully considered a bolt, the lag bolt is actually a type of screw. Also known as lag screws or coach screws, such fasteners have a hexagonally shaped head and externally threaded shank similar to a hex. bolt. Due to having a pointed tip that is commonly seen on conventional screws, lag bolts may form their own holes in a surface through boring. As they form their own hole for a secured attachment, lag bolts can provide extra strength as compared to a carriage bolt. For their construction, lag screws are often composed of a carbon steel substrate that has been coated with zinc galvanization for the means of deterring corrosion. While such fasteners are considered screws, many tradesmen continue to refer to the components as bolts due to their large hex heads or square heads. For establishing a bolt assembly with a lag bolt, such fasteners are most commonly relied on for lagging together lumber framing, lagging machinery feet to wooden surfaces, and other various carpentry applications.

While screws and bolts are considered two separate fastener types, they do share some similarities. For one, both components typically feature a head on one end of the shaft and external threading. Additionally, the heads of screws and bolts will often share similarly shaped recesses, commonly permitting the use of the same tools for installation and removal. Their major difference, however, is how they tend to be installed into a surface for assembling components. With a screw, the pointed end of the shaft allows the screw to create and secure an assembly by itself. With a bolt, on the other hand, a preformed hole is required for installation and the bolt cannot be secured without the use of some form of mating threading such as is provided by a nut.

When choosing between fasteners, it is important that one considers the materials that they are working on so that an accommodating fastener may be used. Additionally, the material of the fastener is important as well, due to the fact that some applications may present risks of corrosion, heat extremes, and other environmental factors that can be detrimental to certain materials. When it comes time to begin sourcing the various fasteners that you need for your particular project, look no further than Sourcing Streamlined.

Sourcing Streamlined is a trusted supplier of various aviation components and aircraft parts, and we are your solution for top quality fasteners. Whether you are searching for parts that are new, used, or obsolete, our unrivaled inventory of over 2 billion items has everything you need. Take the time to peruse our catalogs, and we invite you to send us a completed RFQ form to request quotes for your comparisons. If you have any questions regarding our offerings or would like to begin the purchasing process, give our team members a call or email today and they would be more than happy to assist you as needed.


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April 22, 2021

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