M8 bolts are used throughout a bike for a variety of purposes. They are commonly found in brake caliper retaining bolts, derailleur mounting bolts, quill stem bolts and seat post bolts.
Determining the necessary tapping hole size is simple when the metric bolt diameter is subtracted from the thread pitch. A typical coarse thread has a pitch of 1.25, so the required tapping drill is 6.75mm.
Length
M8 screws are a common screw size that can be used in a wide range of materials. They have a 6mm diameter and a 1mm pitch. M8 screws are not larger than M6 screws, but they have a different type of thread and are used in different applications.
Metric bolts and fasteners are often defined in terms of their shaft diameter, thread pitch, and length. These measurements are given in millimeters, which offer greater accuracy than imperial sizes.
The metric bolt size number can be determined by measuring the shaft diameter of the bolt and comparing it to a chart. You can also determine the bolt size by subtracting the thread pitch from the shaft diameter. It is important to note that if the pitch definition is omitted from the bolt specification then it is assumed to have a coarse thread. This is why it is important to check the bolt specification before use. This will prevent the bolt from being inserted into the wrong hole.
Diameter
M8 is a common bolt size for bicycles, used in many different parts of the bike. For example, it can be found in the brake caliper mounting bolts, derailleur mounting bolts, quill stem bolts, and seat post bolts. The M8 bolt diameter can be determined by measuring the bolt shaft or major diameter. The major diameter is the distance between the threads on the bolt shaft.
Metric bolts are commonly referenced using M-size numbers such as M3, M8, and M12. These sizes are more accurately specified by their diameter, pitch, and length dimensions in millimeters. In contrast, inch fastener sizes are usually described by their major diameter and thread pitch.
When drilling a hole for an M8 bolt, it is important to use the correct diameter to prevent pinching the threads. The optimum tapping drill diameter can be calculated by deducting the thread pitch from the metric bolt diameter. For instance, an M8 bolt with a coarse thread pitch of 1.25mm requires a tapping drill with a diameter of 6.75 mm.
Thread Pitch
The diameter of a bolt’s shaft and the thread pitch are two important dimensions to know. Thread pitch is the distance between the crests of one thread and the root of another. It’s also sometimes referred to as the lead of a thread.
Standardized threads are important to ensure that bolts can mate with nuts without damage or seizing. Until industrialization and mass production allowed for rapid distribution of fasteners, many different thread sizes existed. These incompatible threads led to confusion and problems. Fortunately, World War II fostered cooperation in the area of bolt standardization.
The ISO metric thread size system is an international standard that uses a letter and number to describe the diameter of a screw or bolt. This system includes both coarse and fine threads. The most common bolts use coarse threads, while precision applications require fine ones. In theory, finer threads should provide more tensile strength for the same torque. However, this is not always the case.
Material
When choosing a bolt size, it is important to consider the material as well. Bolts come in a variety of materials, from standard low carbon steel to more robust alloy steel. They can also be zinc plated or black oxide coated to protect them from corrosion.
The most common metric bolt sizes are M4, M5, M6, and M8. For example, M8 bolts use a standard coarse thread pitch of 1.25mm and have a shank diameter of 8mm. Bolts of this size are often used for chainring stack bolts and other components.
The M8 bolt dimensions can be confusing to those unfamiliar with metric fasteners. In addition to the nominal shaft diameter and thread pitch, it is also necessary to know the type of nut that will be used with the bolt. This will determine whether the bolt is a fine or coarse thread and what type of clearance hole needs to be drilled. For instance, a coarse-threaded bolt requires a larger clearance hole than a fine-threaded one.
