Tips to Select the Right Bolt for the Job



While bolts may not seem like a high-tech tool, there are some elements that make finding the right one challenging. Bolts are a type of fastener, and they have been a crucial part of mechanical engineering for decades. Through the years, they have evolved to meet the high-performance demands present today.

While there are a lot of options when it comes to bolt selection on sites like, there are some tips that can make choosing the right bolt easier. Keep reading to learn what these tips are.

Bolt Grade and Class

It is possible to tell a lot about a bolt just by inspecting its head. To figure out if the bolt is American (Imperial or English) or metric, look for the markings located on the head of the fastener. With an American bolt, there will be radial markings to help determine the strength class or grade of the bolt.

To identify the grade for U.S. bolts, look for the total number of radial markings on the head and then add two to that number. For example, Grade 5 bolts have three radial markings on the head. Grade 8 bolts have six radial markings.

With metric bolts, the class number is located on the head. It will be something like 8.8 or 12.9.

Common Challenges Related to Measuring Total Bolt Length

Identifying the bolt classes and grades is something that is somewhat straightforward. There is a more challenging part of bold selection, though, which include measuring the total length of the bolt.

With hex heads, measure under the head to the end of the bolt. For tapered or countersunk heads, measure the total length. Usually, mistakes are made when measuring countersunk bolts. Some people make the mistake of measuring beneath the head to the end of the bolt, failing to account for the countersink depth. This results in the bolt being used being too short.

Measuring the Thread Pitch

This is another challenging aspect. For an American or English bolt, just measure the total number of threads per inch. This is easy, as all a person needs is a ruler for measuring the threads. The number of threads that are in a single inch will let the person know if they are dealing with a fine or coarse thread bolt.

For metric bolts, it is necessary to measure in millimeters from one thread to another. Instead of using a standard ruler, a millimeter gauge is needed. This will ensure that the right measurement is found. A good rule to follow is that smaller fasteners will have finer thread and a lower thread pitch. A bigger bolt will have threads that are farther apart, which means they have a higher thread pitch.

Finding the Right Bolt

When someone needs to find the right bolt for their project or job, keeping the tips here in mind will pay off. Being informed and knowing what to consider when purchasing these fasteners will pay off and ensure the right bolt is used. If you need additional help, contact a hardware professional.


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