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How Does a Carriage Bolt Work?

Updated July 19, 2017

A carriage bolt is a bolt designed to be tightened with only one tool. Carriage bolts are ideal when only one side of an assembly has clearance to turn a wrench. Carriage bolts are commonly used in snow ploughs to attach the cutting edge to the blade.

What is a Carriage Bolt?

A carriage bolt is a bolt designed to be tightened with only one tool. Carriage bolts are ideal when only one side of an assembly has clearance to turn a wrench. Carriage bolts are commonly used in snow ploughs to attach the cutting edge to the blade.

The Design

Unlike the hex cap screw we all normally call a bolt, carriage bolts do not have a hex on one end. Instead, carriage bolts have a dome-shaped head. Under the head is a square area. It is this square that makes it possible to tighten these bolts with only one tool.

How it Works

By itself, a carriage bolt doesn't work as planned. The square area under the head is designed to fit in to a square hole in the workpiece. It is this square hole that restrains the bolt and keeps it from turning when the nut is tightened.

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About the Author

K.K. Lowell is a freelance writer who has been writing professionally since June 2008, with articles appearing on various websites. A mechanic and truck driver for more than 40 years, Lowell is able to write knowledgeably on many automotive and mechanical subjects. He is currently pursuing a degree in English.