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Questions And Answers On Carriage Bolts

Why Are They Called Carriage Bolts?

Carriage bolts were once mainly used on the frames of carriages. This application is where they derive their name. Their square necks are suited to the square holes punched into the wood frame of the carriage.

Today they are used to fasten various metal elements to wood in a range of structures.

What Is The Difference Between A Lag Bolt And A Carriage Bolt?

Carriage bolts and lag bolts differ in their form, although they are both applied to wood applications. Carriage bolts have a domed head, and a consistent cylindrical threaded portion, which ends in a flat edge.

They have a square neck that prevents them from turning once they are installed. Lag bolts have a hexagonal head, wider threaded portion, and pointed head.

Do Carriage Bolts Have Shear Strength?

A carriage bolt’s grade, material, and diameter are key factors in determining the bolt’s shear strength, tensile strength, and weight capacity.

Using grade 8 carriage bolts made from alloy steel as an example, these bolts will provide 90,000 psi shear strength and 150,000 psi tensile strength.

These varied limitations are an important factor when identifying the most appropriate type of carriage bolt for an application.

How Are Carriage Bolts Measured?

When taking carriage bolt measurements, the diameter and length are the main factors. They are taken in the same manner as other types of bolts and threaded fasteners.

The length is the measurement from the underside of the head to the end of the threaded portion. The diameter refers to the width of this portion.

What Are Grade 5 Carriage Bolts?

Grade 5 carriage bolts meet the demands of many construction, industrial, and manufacturing applications that require wood to metal connections.

They are considered in industrial grade and are manufactured with medium tempered carbon steel, which can also be zinc treated. Bolts of this grade provide a tensile strength rating of 120,000 psi.

They also satisfy SAE J429 strength and hardness criteria and ASME B18.5 dimensional specifics.

What Are Carriage Bolts Used For?

The primary function of carriage bolts is to securely connect metal and wood parts. They are often used in lumber- and timber-based structures.

They are suitable for use in such placements as their extended, dome-shaped head contributes to a secure assembly and prevents tension loss and pull-through issues.

What Are Carriage Bolts Made From?

Carriage bolts are usually made from industrial metals like carbon steel, alloy steel, and stainless steel. The materials used in their manufacture are consistent with the standards used in other types of construction bolts.

Carriage bolts may also be treated with various finishes to improve their resistance. These treatments include hot-dipped galvanization and zinc-plating.

Do Carriage Bolts Need Washers?

A washer is not a mandatory part of a carriage bolt assembly. Because they have a wider, dome-shaped head, they will distribute load and are suited for placement in a soft material like wood.

The square-shaped collar below the bolt head will prevent rotation, thus maintaining the tension of the assembly. A washer can still be added if a material barrier is required.

How Do Carriage Bolts Work?

Carriage bolts are used in the fastening of metal elements to wood forms and frames. Their head is rounded and smooth. As a result, they are not tightened from this side but are instead secured from the nut side of an installation using a wrench.

They are placed in pre-drilled holes. They have a square-shaped neck, which prevents them from turning and maintains tension.

How Do You Install Carriage Bolts?

Carriage bolt installation starts with the bolt being inserted into a pre-drilled hole in a wood workpiece. The installation hole should be compatible with the diameter of the bolt.

The square-shaped neck of a carriage bolt prevents it from shifting as the nut is placed on the end and tightened, which is done with a hand wrench or power tool.