Carriage Bolts

What is the difference between carriage bolts & hex head lag screws?

• Carriage bolts have a flat end, whereas hex head lag bolts feature a pointed tip.
• The flat end of carriage bolts can accept a washer & nut for secure installation.
• Lag bolts have wide threads and are screwed directly into wood, without requiring nuts to complete the assembly.

What is the difference between carriage bolts and plow bolts?

• Carriage bolts are generally used in smaller equipment like snowplows attached to pick-up trucks, whereas plow bolts are used in larger plow equipment like excavators.
• Carriage bolts have a flat profile across the bottom of the head, while plow bolts have an angled head for fitting onto countersunk holes.

Why are carriage bolts named so?

Carriage bolts became popular when they started getting used in the manufacturing of carriages & carriage wheels. Thus, they got named 'carriage bolts'.

What does the strength grades / classes mean in carriage bolts?

• The grade or class of a fastener indicates its strength & compatibility with the respective nut / threaded rod / screw / bolt / washer.
• Generally, the higher the grade, the higher the strength of the fastener.
• SAE specifies grades for Imperial-sized carriage bolts. Carriage bolts having the same SAE strength grade as a nut should be used together.
• ISO rates Metric-sized carriage bolts. Carriage bolts having the same first digit as a nut are meant to be used together.
• ASTM grades carriage bolts based on factors like strength, high-pressure & high-temperature application.

How to install a carriage bolt?

• Drill a hole of the appropriate bolt size (diameter) into the surface for sliding the bolt.
• Place the washer & nut on the back side of the bolt (opposite side of the head).
• Tighten the nut to pull the bolt's square shoulder into the surface.
• When the underside of the bolt head rests against the surface, the carriage bolt is completely installed.

How to remove a carriage bolt?

• Twist the nut loose to the end of the bolt. Do not take the nut out of the bolt as it is required to move the bolt.
• Hit the nut using a hammer to move the bolt's square shoulder out of the surface. After some time, the nut would get closer to the surface.
• Repeat the process till the nut no longer grips the bolt or when the bolt can be removed by hand.
• Users can pry the bolt out of the hole using the nail remover attached to a hammer, if the bolt gets stuck in the hole.

Do carriage bolts need washers?

It is highly recommended to use washers with carriage bolts. Using a washer under the screw head increases the surface area and distributes the load. This decreases damage when pulling the bolt through the material using the nut and prevents the bolt from sticking / digging into the surface.

What are some standards that carriage bolts abide by?

Carriage bolts may adhere to international standards like ASME (American Society of Mechanical Engineers), ASTM (American Society for Testing and Materials), ISO (International Organization for Standardization), SAE International (Society of Automotive Engineers) & DIN (German Institute for Standardization) for meeting performance, safety, dimensional & material requirements.