M8 bolt dimensions are regulated by DIN and ISO fastener standards. They are often produced as hot-dipped galvanized steel for corrosion resistance and strength.
Bolt size is based on diameter and thread pitch. The necessary tapping hole size can be easily determined by subtracting the metric bolt diameter from the thread pitch.
Diameter
The diameter of a bolt is the size of its shaft, and it is typically specified in millimeters. Bolts with metric threading are often marked to indicate their diameter and pitch, as well as their length. This helps prevent confusion between imperial and metric bolts, which use different measurements.
Metric bolts are also identified by their thread pitch, which is the distance between adjacent threads. This is often represented by the last number in a bolt’s designation.
When a bolt is to be tapped, the requisite tapping hole size can be calculated by subtracting the thread pitch from the metric bolt diameter. For example, an M8 bolt has a diameter of 8mm, and if it is to be tapped with a standard coarse thread pitch, a hole of 6.75mm must be drilled. However, clearance holes are commonly drilled slightly larger to allow for misalignment and to avoid pinching the threads when clipping the bolt. This allows the threads to have greater load-bearing capacity and strength.
Length
Unlike American bolts, which use diameter and thread pitch to describe their size, metric bolts are defined by their overall length. This measurement can be taken from the base of the head or the point where the shank connects to the threaded part. Typically, the smallest measurement will be taken from the top of the head.
Most metric bolts are stocked with coarse-thread options, but some are also available in fine thread and extra fine thread. The fine-thread bolts tend to be a bit more expensive, but are generally stronger than the coarse-thread ones.
The M8 bolt is a common bolt size on bikes. It is most often used for brake caliper retaining bolts, derailleur mounting bolts, quill stem bolts and seat post bolts. It has an ISO dimension of 8 x 1.25mm and can be screwed or unscrewed using 6mm Allen wrenches or 13mm hexagonal wrenches. You can find more information on metric bolt sizes here.
Pitch
M8 bolts are most commonly used on mountain bikes, though they can also be found in other uses. These bolts have a diameter of 8 millimeters and a thread pitch of 1.25 mm. They can be tightened using 6mm allen wrenches or 13mm hexagonal wrenches. You can find these bolts on brake caliper retaining bolts, derailleur mounting bolts, quill stem bolts, and seat post bolts.
While the metric diameter is easy to measure, the thread pitch can be more difficult to determine unless you have a measuring tool. The thread pitch is the distance between two thread peaks, and it can vary between different sizes of metric bolts.
Many metric bolt measurements fail to include the thread pitch, and this can cause confusion for people who are unfamiliar with metric hardware. However, it is important to check the thread pitch, as it is a defining feature of a fastener. If the thread pitch is not included, it can be deduced from the metric bolt diameter by subtracting the thread pitch.
Thread Depth
Unlike imperial bolts, which are often labeled by their outer diameter, metric bolts have their size measured from the crest of the thread to the root. This measurement is known as the major diameter, and it is the most important one when determining if a nut or bolt will fit into a clearance hole.
The major diameter of an M8 bolt is a little over 8 mm. This means that it will easily fit into a clearance hole of the same size. However, it is important to keep in mind that there are several different types of clearance holes and threads that can be used with this bolt.
Additionally, the tensile stress area of a screw or bolt is correlated with its TPI. Therefore, a screw with a larger TPI will be more robust than a screw with a smaller TPI. This is because a higher TPI allows for a greater number of threads per inch.m8 bolt dimensions