Everything You Need to Know About Carriage Bolts - JM Hardware

11 Aug.,2025

 

Everything You Need to Know About Carriage Bolts - JM Hardware

Introduction:

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When it comes to assembling various structures and ensuring their stability, carriage bolts play an integral role. These robust yet versatile fasteners are widely used in a range of applications, from woodworking to construction projects. In this comprehensive guide, we will delve into every aspect of carriage bolts to provide you with a complete understanding of their features, applications, and benefits. Whether you are a DIY enthusiast or a professional contractor, this article will equip you with the knowledge required to confidently work with carriage bolts.


The Origins of Carriage Bolts

Carriage bolts, also known as coach bolts or round head square neck bolts, have a fascinating history dating back centuries. They were initially developed for use in the carriage-building industry during the 19th century. Their unique design, with a round, domed head and a square neck section beneath, made them perfect for holding wooden components together in horse-drawn carriages. Over time, their application expanded to other industries due to their reliability and strength.


These bolts were specifically designed with a square neck to prevent them from rotating when tightened. The square neck fits into a correspondingly-sized hole in the material, ensuring the bolt remains secure during installation. This feature significantly simplifies the assembly process as it provides stability and prevents the bolt from turning, making them suitable for applications where access to both sides of the joint is limited.


The Anatomy of Carriage Bolts

To fully comprehend the functionality and applications of carriage bolts, it is essential to understand their unique anatomy. A typical carriage bolt consists of four main components:


1. Head: The head of a carriage bolt is circular and domed, featuring a shallow, sloping shape. This design allows for easy installation using hand tools or power tools, providing a smooth, finished appearance once fastened.


2. Shank: The shank of a carriage bolt refers to its long cylindrical body. This section is smooth, with a threaded portion towards the end. When selecting a carriage bolt, it is crucial to ensure that the length adequately accommodates the materials being fastened.


3. Square Neck: The square neck, located beneath the head, is a distinctive feature of carriage bolts. It prevents the bolt from rotating while tightening the nut. This design is particularly advantageous when working on projects where accessing both sides of the assembly is challenging.


4. Thread: At the base of the shank, carriage bolts have a threaded section. The thread allows for a secure connection by gripping the material tightly. With a firm hold, carriage bolts can withstand significant weight and pressure, providing structural integrity to the joined components.


Different Types of Carriage Bolts

Carriage bolts are available in various types, each designed to cater to specific applications and requirements. Understanding the different types will enable you to choose the appropriate carriage bolt for your project. Here are some common variations:


1. Round Head Carriage Bolts: This is the standard type of carriage bolt, characterized by its round head and square neck. It is widely used in woodworking applications, such as furniture assembly and deck construction.


2. Mushroom Head Carriage Bolts: As the name suggests, these bolts feature a head that resembles a mushroom shape. This variant offers a larger surface area compared to round head carriage bolts, resulting in improved load-bearing capacity.


3. Ribbed Neck Carriage Bolts: Ribbed neck carriage bolts have continuous, shallow ridges along their square neck section. This design enhances gripping power, making them ideal for applications where vibration resistance is essential.


4. Tension Control Bolts: Tension control bolts, also known as TC bolts, are a specialized type of carriage bolt. They feature an oval-shaped neck that shears off at a predetermined torque level. This design eliminates the need for torque monitoring and ensures accurate tension control during installation.


5. Grade 8 Carriage Bolts: Grade 8 carriage bolts are manufactured from heat-treated alloy steel, offering exceptional strength and durability. They are commonly used in heavy-duty applications that require high tensile strength and resistance to corrosion.


The Applications of Carriage Bolts

Carriage bolts find extensive use in a wide range of applications across various industries. Some of the common uses include:


1. Woodworking: Carriage bolts are widely employed in woodworking projects, such as furniture construction, framing, and cabinetry assembly. The square neck prevents rotation during installation, ensuring a secure and stable joint.


2. Construction: In the construction industry, carriage bolts are used for applications that involve joining wooden beams, posts, or planks together. These bolts provide robust connections, ensuring structural integrity in projects like deck building, timber framing, and roof construction.


3. Automotive: Carriage bolts are employed in the automotive industry for various purposes, including securing body panels, seats, engine components, and suspension parts. They provide a reliable and secure fastening solution that can withstand the vibrations and stresses associated with vehicles.


4. Machinery and Equipment: Carriage bolts are utilized in the assembly of machinery and equipment across different industries. From agricultural machinery to industrial equipment, these bolts play a crucial role in ensuring the integrity and safety of the assembled structures.


5. Infrastructure: Carriage bolts are an essential component in the construction and maintenance of infrastructure projects, such as bridges, highways, and railways. They are used to join concrete and steel components, providing the necessary strength and stability required in these structures.

Are you interested in learning more about Custom Carriage Bolts? Contact us today to secure an expert consultation!


In Summary

Carriage bolts are an indispensable fastening solution for a wide range of applications, offering strength, stability, and ease of installation. Whether you are working on a woodworking project, construction endeavor, automotive application, or any other task that involves joining materials together securely, carriage bolts are an ideal choice. Understanding the anatomy, types, and applications of carriage bolts empowers you to select the right bolt for each project, ensuring long-lasting and reliable results. So, next time you embark on a project that requires sturdy connections, remember to consider the versatile and dependable carriage bolts.

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Carriage Bolts | mfsupplyblog - MF Supply's

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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