Nuts and bolts come in a variety of types, and each one is designed for a specific purpose. Each nut and bolt is different because of the type, diameter, pitch -- or thread count -- and length. Once the type of the bolt or nut is determined, then the diameter, pitch and length are considered for the right fit.
Lay a bolt on a flat surface. Use a magnet to determine whether the bolt is steel or stainless steel. If the bolt sticks to the magnet, then it is steel; if the bolt does not stick, then it is stainless steel or another type of metal.
Determine if the bolt is a grade 2, 5 or 8. A grade-2 bolt will have a six-sided head with no markings on top of the bolt head. A grade-5 bolt will have a six-sided head with three lines etched into the top of the bolt head. A grade-8 bolt will have a six-sided head with six lines etched onto the top of the bolt head.
Determine the diameter of the bolt with a measuring tape. The diameter is the width of the threads. Write down the diameter on a notepad.
Measure the pitch count with the measuring tape and write the number on a notepad. The pitch count is the number of threads on the bolt.
Measure the length of the bolt with the measuring tape and write the number on a notepad. Measure the length of the bolt from under the bolt head to the end of the bolt.
The numbers on the notepad tell you the bolt diameter, pitch count and length. Say, for example, your numbers are 1/4, 20 and 1 1/2. This means that the bolt diameter is 1/4-inch, the pitch is 20 threads and the length is 1 1/2 inches.
Determine a nut type by measuring the diameter and the height of the nut. The diameter is the inside width of the nut and the height is the length from the bottom of the nut to the top. Place the nut on a flat surface and take the measurements. Write down the diameter and the height on the notepad.
Most bolts are glazed with zinc or chrome. Use a bolt and nut chart to also determine the proper size and type.
Wear gloves if necessary when handling bolts to prevent cutting your fingers on the bolt threads.