M8 Bolt Size and Thread Pitch

Using a set of digital calipers or micrometer is the best way to accurately measure a bolt’s shaft diameter. This will help ensure that the correct nut is used for your application.

Bolt dimensions are usually designated in a three-digit format, such as M8-1.0*20. These numbers represent the metric thread designation, shaft diameter, and the thread pitch.
Diameter

The diameter of an M8 bolt is around 8 millimeters. It is the same as the diameter of a standard 5/16 bolt or screw. The M8 bolt size is a common one, and most clamps that come with a hex bolt also have this standard bolt size.

In the US, bolt sizes are typically measured in inches using a tape measure. The measurement is taken by counting the smallest lines on the tape and adding up the number of sixteenths. This is referred to as the Whitworth system of measuring fastener size.

However, in the world of metric bolts, the diameter of the shank is indicated by the letter M followed by the number, and the value after the x denotes the thread pitch. A coarse thread means the threads are thicker, while a fine thread is narrower. The nut height will be roughly 80% of the shaft diameter, but clearance holes are often drilled a little larger to allow for misalignment.
Length

An M8 bolt has a shaft diameter of just under 8 millimeters. This is a standard metric bolt size. Bolts with a smaller diameter are usually used in larger holes. It’s common to drill clearance holes that are a bit larger than the actual bolt to allow for misalignment.

For metric fasteners, the length is described by subtracting the thread pitch from the nominal bolt diameter. This is different from the way American bolts are measured.

The height of flat head, cheese, pan and hex bolt heads also affects the length of a bolt. When you need to measure the length of a bolt, you should do so from the underside of its head. You can use a ruler, tape measure or caliper to do so. You can also measure the thickness of the head. This is known as the bolt’s head thickness. It’s important to know this before purchasing a bolt. You can purchase the wrong hardware if you don’t.
Thread Pitch

The thread pitch is the distance between one thread groove and the next. This can be determined by using tools such as digital vernier calipers or a thread gauge. There are 4 different thread pitches for metric bolts, including standard (sometimes referred to as coarse) and fine or extra-fine. It is important to know the correct thread pitch to ensure that your bolt will fit correctly.

If the thread pitch is not included in the specification for a metric bolt then it can be assumed that the bolt will have a coarse thread. However, the pitch must be specified if it is required. The different thread pitches also have varying strengths, with the higher strength grades being able to carry more load than the lower strengths. This can be helpful when designing components that will need to be fastened together with a bolt. This is to help prevent the threads from stripping due to excessive tightening or stress.
Material

The material used to make an M8 bolt is generally 304 stainless steel. This steel has decent corrosion resistance and has good tensile strength. This bolt is typically marked with the number 8.8, 10.9, or 12.9. These numbers indicate the tensile strength of the steel in the bolt.

When choosing a bolt, it is important to consider the thread type and its load bearing capacity. The tensile strength of the bolt is determined by the load per square millimeter of the cross-section. This is measured in Newtons.

Metric bolts have a diameter, pitch, and length associated with their size. If the pitch is not indicated, the bolt is usually coarse threaded. This allows for faster installation and removal of the bolt from the fastener hole. To determine the nut size, subtract the bolt shaft diameter from the metric thread pitch. Then, divide the result by 16 to get the nut size. This method works for hex, cheese, pan, and low socket heads as well as nyloc and dome nuts.