What Are Carriage Bolts And Everything Else You Need To Know

What Are Carriage Bolts And Everything Else You Need To Know

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You should know that the carriage bolt screw has been around for many centuries. However, these fasteners gained popularity during the early 1800s since they were extensively used for building carriages and carriage wheels. Also, this is how the bolt got its name. Carriage bolts are also referred to as carriage screws, coach bolts, and round-head square-neck bolts. In New Zealand and Australia, carriage bolts are also called cup head bolts.

What are the types of carriage bolts?

Carriage Bolts come in different types with different head styles. Some of the commonly used types of carriage bolts are as follows.

  • Ribbed neck, round head carriage bolts:

    These bolts are built from carbon steel. These types of carriage bolts are characterized by shoulders that are serrated or ribbed with a round head. These carriage bolts are primarily utilized for fastening wood, plastics, and/or soft and ductile metals.

  • Short neck, round head carriage bolts:

    Characterized by a round head and a short and square-shaped shoulder, these bolt types are built from low or medium carbon steel. The thread pitch on the short neck and round head carriage bolts are unified. These carriage bolts are suitable for fastening owing to their short neck that helps create an obstruction.

  • Square neck, flat head carriage bolts:

    These carriage bolts get their name from their flat head. The flat head helps in providing a low profile on the top or front side of fastening as compared to that of a round head bolt. Square neck, flat head carriage bolts are mainly built for but are not limited to applications in the garage door industry.

  • Fin neck carriage bolts:

    These carriage bolt fasteners are generally built from low carbon steel material. Featured with a round head and a flat bearing surface the carriage bolts make a 90° angle with the shank. The fin neck bolts are mainly used in thin plywood.
    It is important to remember that carriage bolts are measured along their entire length, right from underneath the head, including the square neck. Don’t make the mistake of measuring from under the neck - this is a common error.

What are carriage bolts used for?

Carriage bolts are mostly designed for securing wood to metal, metal to metal, or wood to wood. Today, carriage bolts are most commonly applied for carpentry and wood construction. Homeowners and professional carpenters often use Carriage bolts for home maintenance, DIY projects, and repair work. Other than that, some other carriage bolt uses are also seen in different industries like the railroad, water conservation and treatment, mining, and farming.
Carriage bolts are also painted black sometimes. Black carriage bolts are designed for securely fastening galvanized or powder-coated parts. Carriage bolts made from stainless steel are the most popular. Stainless steel carriage bolts are highly anti-corrosive and work excellently even in extreme environmental conditions. Other than that galvanized carriage bolts are also available and used for fastening decks, docks, gaming equipment, fencing, and/or furniture.
Using carriage bolts calls for the use of a few additional tools like a hammer, drill, drill bit, nut, and/or washer. Washers are an important component for use with carriage bolts since they prevent damage when using the nut to pull out the bolt through a material.

How to use carriage bolts?

Follow the steps below to successfully install a carriage bolt into your intended surface.

  1. Measure the diameter and length of the chosen carriage bolt by using a measurement tape.

  2. Get a drill bit, the same size as the carriage bolt. Not getting the size right might hamper the proper installation of the bolt. A larger bit can result in a loose bolt and a smaller bit will not allow the carriage bolt in. This is also the reason why carriage bolts should not be inserted into pre-drilled holes. Always remember, to use cutting fluid to cover the drill bit when making a hole on the surface of the metal to make the task easier.

  3. The next step is to dig a hole into the surface of the material where the carriage bolt has to be installed. While digging, remember to run the drill at a slower RPM. This allows us to dig the hole smoothly on the harder surfaces while also giving you more control.

  4. Insert the carriage bolt into the drilled hole. If the hole is congested, you can use a hammer to slightly force the bolt in.

  5. After putting the bolt into the hole, you can complete the installation of the carriage bolt. Place a washer on the opposite side of the bolt and then put the nut on it. Roll over a nut on the bolt and tighten that up using a wrench. The square shoulder on the bolt will prevent it from spinning on the material.

Remember to follow the installation steps accurately to get a stronger bond between the different parts of the element. You can remove the carriage bolt by twisting the nut, while also ensuring that it remains on the bolt. Also, carriage bolts and nuts must both be of the same size for achieving the right level of fastening.


KG Lilly Fasteners has been one of the industry-leading carriage bolt suppliers in America. Every single carriage bolt we supply is made with the most advanced machinery and with the utmost precision.

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