What are Anchor Bolts?

Mary McMahon

Anchor bolts are cylindrical fasteners that are used to connect objects and structural elements to concrete. They may be used for everything from holding a home to its foundations to attaching heavy industrial machinery to a factory floor. Many manufacturers make these bolts, and there are several different styles available for different applications. When installed correctly, they form a very firm, solid connection that will last for decades. Anchor bolts can be purchased in some hardware stores and through construction supply companies as well as manufacturers.

Various nuts, bolts and screws.
Various nuts, bolts and screws.

The classic version is a cast in place anchor bolt. These bolts are inserted into concrete while it is still wet, with the threaded part sticking up. When the concrete hardens, the bolt is set in place, and objects can be bolted down with the use of a nut that connects to the threaded section. These bolts are often used in new construction projects, where the location of walls and other elements that need to be connected to the foundation is well known.

The other type is a bolt that is inserted into the concrete after it sets. These bolts require a drilled hole, and they can be fastened in place with epoxy or with a wedge that expands to trap the bolt when it is tightened. For retrofitting and similar tasks, these bolts can be very useful, although it is important to install them properly or they may fail, sometimes catastrophically.

When anchor bolts are used in construction, the builder must usually abide by local building codes, which dictate the size of the bolts and the necessary distance between them. The goal is to distribute the load of the construction over multiple points, reducing the amount of stress on any particular bolt or any given area of concrete. An engineer or architect may calculate the stress and loads involved to make sure that the bolts are placed appropriately.

The major drawback to these bolts is that once they are in place, they cannot be removed without jackhammering out a section of concrete. In a situation where the bolts are critical construction elements, this is usually not a major issue, but it can be a problem when anchor bolts are used to secure heavy machinery. If a factory is reconfigured to produce something different, for example, the old fasteners may be in the way.

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Discussion Comments


Steel anchor bolts can be very dangerous to make as well, depending on what specific kind of machine that you use. I was unlucky enough to find this out first hand.

I was working in a metal fabrication shop and using on an older machine called a kinefac some years ago. The rods I was working with had some slight twists to them. I was new and didn’t think that it was a real big deal – until the rod jerked and somehow my glove got caught; my whole arm was pulled up into the machine.

I ended up being okay, but I did some damage that I’ll always have to deal with. The ligaments and muscles were torn up pretty badly, and the machine itself actually stretched my skin and now I’ve got permanent stretch marks under that arm. I will never regain one hundred percent usage of that arm again, but I’ve still got about eighty.

It could have been a lot worse, though, so I’m thankful.

Like they say, the best thing to do is get up and go again. I was back at work the next day on that same old kinefac.


My husband actually used to be an iron worker in Bristol, TN and made anchor bolts for a living. Now, naturally, that wasn’t all that the shop that he worked at made, but that was a big thing at the time.

I remember it well, because when we first met he was in this line of work while going to school part time at the town's local college. Good gracious, ladies! If you want a man that you can climb like a tree, go with an iron worker!

Anyway, I remember these galvanized anchor bolts specifically because he talked about them constantly for about a year. You see, there was a NASCAR track in Bristol and he was personally making all of the anchor bolts that they needed to expand the stands that the spectators sit in.

Imagine a high school football stadium and then expand it by about 10. There you go, and probably three or four times as tall.

I always thought that it was amazing that my then boyfriend, now husband, had the ability to make something like that! I mean, there have been millions of fans in those seats since then and my husband made sure they all had a safe place to enjoy their races! That takes skills, people!

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