What Is a Carriage Bolt?

Carriage bolts, also known as coach bolts or plow bolts, are special fasteners used to securely hold materials together. They are easily recognizable by their smooth, rounded (domed) head and square neck directly beneath the head. This unique design allows the bolt to lock into place when inserted into pre-drilled square holes, preventing it from rotating when the nut is tightened.

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Carriage bolts are commonly used in woodworking, metalworking, and construction, where a clean, snag-free surface is important. They are ideal for applications where the fastener needs to be concealed or where a smooth finish is essential.

Types of Carriage Bolts

Carriage bolts come in several types, each designed for specific applications. Below are the main types:

Long Neck Carriage Bolts
Long neck carriage bolts come with an extended neck, which is sometimes partially threaded. These bolts are ideal for connecting larger or thicker components. The extended neck offers more flexibility when fastening materials of varying thicknesses.

Standard (Square Neck) Carriage Bolts
These are the most commonly used carriage bolts. They have a round, domed head with a square neck underneath. Versatile and widely used, these bolts are ideal for general-purpose fastening in woodworking and construction projects. Available in materials like steel with zinc plating, galvanized, black oxide, and stainless steel finishes.

Ribbed Neck Carriage Bolts
Ribbed neck carriage bolts feature ribs or ridges around the neck, rather than the traditional square neck. This design improves grip and prevents the bolt from turning when tightened. Ribbed neck bolts are especially useful for applications that require additional stability, such as fastening sheet metal.

Short Neck Carriage Bolts
These bolts have a shorter neck, making them perfect for fastening thinner materials. They are typically used when a standard-length neck would be too long or obstructive. Short neck carriage bolts are suitable for medium to low-strength connections.

Choosing the Right Material for Carriage Bolts

Stainless Steel Carriage Bolts
Stainless steel is a great choice for carriage bolts that will be used outdoors or in marine environments. It resists rust and corrosion very well and gives a clean, shiny finish. Stainless steel bolts are often used in areas that face harsh weather or for decorative purposes. Common types include 304, 316, and duplex stainless steel, each with varying levels of corrosion resistance.

Carbon Steel Carriage Bolts
Carbon steel is known for its strength and toughness, making it ideal for heavy-duty applications. These bolts are usually coated with hot-dip galvanizing or black oxide to prevent rust and corrosion. Carbon steel bolts are widely used in industrial, automotive, and construction projects because they offer both strength and flexibility.

Aluminum and Brass Carriage Bolts
Aluminum and brass bolts are lighter, making them ideal when weight is a concern or when lower strength is acceptable. Aluminum bolts are especially useful in industries like aerospace, where lightweight components are essential. Brass bolts are often chosen for their decorative appearance and excellent resistance to corrosion.

How to Choose the Right Carriage Bolt？

Choosing the right carriage bolt is an important decision that depends on a few key factors. Here’s what you need to keep in mind:

First, think about the material you need. If the bolt will be exposed to the outdoors, stainless steel is your best bet because it resists rust and corrosion. This makes it ideal for marine environments or outdoor furniture. For industrial applications, carbon steel is a great choice, as it’s strong and more cost-effective. If weight is a concern, aluminum or brass bolts might be better. These materials are lighter while still offering reliable performance.

Next, consider the size of the bolt. Carriage bolts come in various lengths and diameters, so it’s crucial to choose the right one. To ensure a proper fit, check the size of the hole you are fastening. The diameter of the bolt should match the hole’s size, and the length should be long enough to go through the materials you’re joining. If you are working with thicker materials, you may need a longer bolt.

Lastly, think about the strength needed for your project. For heavy-duty applications that require a strong hold, carbon steel bolts are the way to go. They provide the strength needed for tough jobs. For lighter tasks, aluminum or brass bolts should suffice. If you’re uncertain about the required strength, it’s safer to opt for a stronger bolt to ensure a secure connection.

Common Uses of Carriage Bolts

Carriage bolts are highly versatile and widely used across different industries. Here are some of the most common applications:

Security Applications
Carriage bolts are also used in security applications. The square neck design prevents the bolt from being turned from the head side, which ensures the bolt can only be removed from the nut side. This feature makes them perfect for gates, fences, and other security-related structures.

Woodworking and Timber Construction
Carriage bolts are commonly used in woodworking projects such as decks, docks, outdoor furniture, and wooden bridges. Their smooth, rounded head ensures a clean, snag-free surface, which is essential in these types of applications.

Metal to Wood or Metal to Metal
These bolts are perfect for fastening metal to wood or metal to metal. They are often used in automotive assembly, trailer construction, and heavy machinery. The square neck prevents rotation, ensuring a strong and secure connection that holds up under stress.

Outdoor and Marine Applications
Stainless steel carriage bolts are particularly valuable in outdoor and marine environments where corrosion resistance is essential. They are commonly used in boats, docks, piers, and other structures exposed to water and harsh weather conditions.

Agricultural and Industrial Equipment
Carriage bolts are frequently used in agricultural machinery, industrial equipment, and infrastructure projects. Their durability and ability to create secure, long-lasting connections make them ideal for heavy-duty applications.

Playground Equipment
The smooth, domed head of carriage bolts is ideal for playground equipment, where safety is a top concern. This design reduces the risk of children’s clothing or skin getting caught, making carriage bolts the preferred choice for building play structures.

FAQ

Are there different grades of carriage bolts?

Yes, carriage bolts come in different grades, which refer to the strength of the bolt. Common grades include Grade 5 and Grade 8. Grade 8 bolts are stronger and typically used for high-stress applications.

What is Grade 8 carriage bolt?

A Grade 8 carriage bolt is a high-strength bolt commonly used in heavy-duty applications. It is made from alloy steel and has a higher tensile strength compared to standard bolts. These bolts are often used in automotive, industrial, and construction applications where maximum strength is required.

What are the types of bolts?

There are many types of bolts, including anchor bolts, arbor bolts, blind bolts, carriage bolts, elevator bolts, eye bolts, flange bolts, and serrated flange bolts.

When should I use a carriage bolt?

Carriage bolts should be used when a smooth, flush surface finish is needed, such as in furniture assembly, attaching metal brackets, or connecting wood to metal or wood to plastic.

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What are the names of carriage bolts?

Carriage bolts are also known by several other names, including coach bolts, round head square neck bolts, mushroom head square neck bolts, dome head bolts, cup head bolts, and plow bolts.

Conclusion

Carriage bolts are an essential and versatile fastening solution used in a wide variety of industries. With their unique design, which prevents rotation and ensures a smooth, secure finish, they are ideal for woodworking, metalworking, construction, and outdoor applications. Whether you are working on a deck, assembling machinery, or building playground equipment, carriage bolts provide the strength and safety you need.

Inch & Metric Carriage Bolts Now Available at www.mfsupply.com!

In the realm of industrial manufacturing and engineering, Carriage Bolts often go unnoticed, yet they play a pivotal role in ensuring structural integrity and reliability. This versatile fastener, commonly known for its unique design featuring a rounded head and a square shank, is a cornerstone in a myriad of applications, such as construction and industrial projects. But just like many other popular fasteners, one size isn’t the right fit for all applications, and this is also the case with Carriage Bolts. So how do you make the right choice?

In today’s blog we will enlighten you about the key aspects of Carriage Bolts, covering their unique features, standards, materials, sizes, strengths/grades, uses and anything else you should know before setting off to buy them for your next big project!

What are Carriage Bolts?

Commonly used in industrial manufacturing and construction, they are ideal for metal-to-metal or metal-to-wood connections, providing a secure and aesthetically pleasing joint. Available in various materials like carbon steel, stainless steel, and alloy steel, and conforming to specific standards like ASME 18.5, SAE J429 and DIN 603 carriage bolts come in a range of sizes and grades to suit different mechanical and environmental requirements. Their versatility and reliability make them a staple in heavy-duty applications where robust fastening is essential.

Who Uses Carriage Bolts?

The robust nature of Carriage Bolts makes them an indispensable asset in many sectors, each valuing their unique combination of strength, security, and aesthetics.

• Construction and Building Industry: In the construction and building industry, they are essential for timber framing and outdoor decking, ensuring durability and safety.
• Automotive and Heavy Machinery Sectors: The automotive and heavy machinery sectors rely on them for vehicle assembly and manufacturing robust equipment.
• Marine and Coastal Applications: In marine and coastal applications, particularly, stainless steel Carriage Bolts are prized for their resistance to saltwater corrosion, vital in boat building and dock construction.
• Railway Industry: Their use also extends to the railway industry for maintaining railway lines and infrastructure.
• Aerospace Industry: Even in aerospace, though less common, Carriage Bolts find a place in non-critical applications, appreciated for their ease of installation and tamper-resistant design.

Whether you’re in construction, automotive manufacturing, aerospace or marine applications, Carriage Bolts play a pivotal role, underscoring their versatility and the trust placed in them by many professionals. Remember, when you’re choosing Carriage Bolts, you’re not just buying a component; you’re investing in the integrity and longevity of your entire project.

What Styles, Standards, Materials, Finishes & Sizes Are Available?

Carriage Bolts’ Styles

The world of Carriage Bolts is vast and varied, catering to a wide range of applications. Understanding this diversity is key to selecting the right bolt for your project. The traditional round head and square neck style is commonly used, but there are other types like Ribbed Neck or Knurled Neck bolts, which offer extra grip. Short Neck variants are useful in tight spaces, while Shaker Screen bolts are designed to withstand high-vibration environments. For specific fitting requirements, Under Sized Body bolts might be the solution, and Flat Head Carriage Bolts are ideal when a flush surface finish is needed. This variety demonstrates how specific designs cater to unique functional needs.

Quality Standards

Carriage Bolts are manufactured according to various quality standards, such as ASME 18.5, SAE J429, and DIN 603. These standards ensure consistency in dimensions, strength, and durability. They also play a crucial role in ensuring that carriage bolts meet the necessary safety and performance requirements across different applications. For instance, a bolt compliant with these standards would have reliable tensile strength and dimensional accuracy, making them suitable for a range of uses from construction to machinery assembly.

Materials

Different materials are used in the manufacturing of Carriage Bolts to suit various environmental and mechanical demands.

• Low Carbon Steel Zinc: Commonly used for standard Carriage Bolts. The zinc coating provides a layer of corrosion resistance. Offers a good combination of tensile strength and ductility, making it suitable for light to medium load applications.
• Grade 5 Steel: Contains a higher carbon content than low carbon steel, resulting in increased strength. Often used in automotive and construction applications where higher strength is needed. Provides a good balance between strength and flexibility, making it less likely to break under high stress.
• Grade 8 Steel: Contains an even higher carbon content than Grade 5, offering superior strength and hardness. Commonly used in demanding applications like heavy machinery and military equipment. Ideal for applications where the bolt must withstand high stress or sudden impact without deforming.
• Stainless Steel 18-8: Composed of approximately 18% chromium and 8% nickel, hence the name 18-8. Offers excellent resistance to corrosion and oxidization. Widely used in environments where exposure to water, chemicals, or saline is common.
• Stainless Steel A2: Similar to 18-8 stainless steel but with slight variances in the alloy composition. Common in food processing equipment and outdoor furniture. Resistant to corrosion and staining, making it ideal for aesthetic applications as well.
• Stainless Steel A4: Also known as marine grade stainless steel. Contains higher levels of nickel and added molybdenum for enhanced corrosion resistance. Ideal for use in highly corrosive environments such as marine, coastal, and tropical climates.

Finishes

The finish of a carriage bolt not only affects its appearance but also its functionality, especially in terms of corrosion resistance. Black Oxide and Black Zinc finishes offer a degree of corrosion resistance along with an aesthetically pleasing look. For environments with high moisture, Hot Dip Galvanized bolts are an excellent choice for their superior corrosion protection. Zinc-Plated and Zinc-Yellow finishes are also popular, offering a balance between corrosion resistance and affordability. Understanding these options is essential for selecting a bolt that not only fits the technical requirements but also withstands environmental conditions.

Sizes Available

The size of a carriage bolt is also another critical factor in ensuring its effectiveness in a given application. The range of sizes available is extensive, from 6-32 through 7/8-9 for inch sizes to M5-0.8 through M12-1.75 for metric DIN 603 sizes. This broad spectrum of sizes accommodates everything from large-scale industrial needs to smaller, custom projects. Selecting the appropriate size is vital for the bolt’s performance, as it affects the strength of the joint and the overall integrity of the project.

How to Order Them

On our website, navigate to the Search bar and type “Carriage Bolt,” and hit the Search Button.

Once the results are listed and the filter appears on the left of the results page, select your desired attributes to get the specific Carriage Bolt(s) you need. Common attributes available in our filters include:

• Inch or Metric
• Head Style
• Size (Diameter & Thread)
• Length
• Material
• Finish
• Other Type (Full or Partial thread or Flank Degree)
• Standard (ASME, SAE, DIN)

Carriage Bolts at MF Supply

MF Supply is a WBE/WOSB certified business, and a trusted supplier of Carriage Bolts to manufacturers, government and industry. At MF Supply, we understand the dynamic needs of the manufacturing industry, including the balance of price, quality, availability and certification paperwork. The expansion of our product catalog to include Carriage Bolts in a myriad of styles, materials, and sizes demonstrates our commitment to being a one-stop solution for all your fastener needs.

Visit our website or browse through the links provided below to discover the perfect Carriage Bolt(s) for your next project!

• Inch Carriage Bolts
• Metric DIN 603 Carriage Bolts
• Please send a Request for Quote for any other Carriage Bolt(s) not listed on our website.

Do you still have questions or would like to speak with a representative? Reach out to us, and our MF Supply team of sourcing experts will help you find what you’re looking for. “Finding the right screw for you” is our tag line after all!

Book a one-on-one consultation with our President, Robin, to discuss how MF Supply can help you solve your Industrial Sourcing, Fastener, and Safety concerns.

Six Reasons To Buy From MF Supply

• Full eCommerce Enabled Website With Technical Manual Available 24/7 – Visit our website and Create a New Account, track online orders, browse our product catalog, check technical specs, subscribe to our blog, or buy online.  We are adding items and improving functionality daily!
• Same Day Shipping From The USA – Our hardware products are in stock and ship to you directly from our USA based distribution centers.
• Functional Equivalents To Expensive Brand Names- We stock and source alternatives to brand name fasteners, reducing long lead times and saving you money.
• Creatively Solve Problems – We are sourcing experts and specialize in hard to find parts. We offer custom manufacturing and reworking solutions at competitive pricing, reducing long deliveries.
• One-Stop Shopping On Certified Hardware – We stock and source a full line of fasteners including Mil-Spec, DFARS compliant and other industrial products.
• WBE/WOSB Woman Owned Certified Small Business – To meet your diversity & set-aside needs.

MF Supply is a WBE/WOSB certified supply chain partner to business, industry and government.  We are sourcing experts and stocking distributors of Hardware, Precision & Mil-Spec Fasteners and Safety supplies.  For more than 50 years, we have been supplying manufacturers in the electronics, industrial, commercial, aerospace and military markets with the full range of fastener products and services.  Our Cage Code is 58QG4 and our registered name is RL Supply Inc dba MF Supply. 

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