The M8 bolt size is the size of a metric fastener that has a threaded section and can be used to hold other hardware, such as nuts, in place. Metric fasteners are usually specified using their diameter, pitch, and length dimensions in millimeters. This is different from American measurements of bolts, which are typically described by their thread pitch and thread diameter.
A M8 bolt is a metric screw that has a shaft with a nominal diameter of 8 millimeters. The metric bolt also has a thread that is 1.25 mm wide. It is also important to know that the M8 bolt has a very shallow depth of thread. This is due to the fact that the threads are hex-headed, and only a small portion of the bolt is actually threaded. This means that clearance holes are often drilled a little larger than the nominal bolt size to ensure that they don’t interfere with any threaded parts.
Bolt size and specifications are essential to the proper use of hardware. If a bolt isn’t of the correct strength, it can cause damage to equipment or create unsafe conditions. Whether you need to determine the size of a bolt to make sure it will fit a hole or to calculate the requisite tapping hole diameter for a tapped bolt, knowing the right information will save you time and hassle.
Metric bolts are often labeled with their diameter, thread pitch, and length in a standard format known as DIN or ISO. The letter M indicates that the bolt uses a metric thread and the number specifies the thread diameter in millimeters. The length of a metric bolt is expressed in the format dnom + 1.0 (where dnom is the nominal bolt diameter, 1.0 is the thread pitch, and dnom+2.0 is the overall bolt length).
In addition to a standard hex bolt head, metric hex bolts can be found with different types of heads. Most commonly, you will see them with a square or hex head. Other options include a cone or torx head. Many hex bolts have a raised lip around the head to prevent the head from falling off during tightening.
The class number printed on the head of a hex bolt is an indication of the tensile strength or breaking strength of that bolt. The higher the class number, the stronger the bolt. The tensile strength is determined by the amount of stress that the bolt can endure before it begins to stretch.
In the US, the tensile strength of a bolt is indicated by the ‘grade marks’ that are printed on the head of the bolt. While these aren’t required in the metric system, they can help you differentiate between bolts that have similar appearances. The ‘grade marks’ are nothing more than numbers that indicate the maximum stress a bolt can withstand without stretching. A grade 12.9 bolt can handle up to 175,000 pounds of force before it begins to stretch.