What Size Is A M8 Bolt?

Hex Socket Bolt, M8×30mm Allen Head Screw, A270
Hex Socket Bolt, M8×30mm Allen Head Screw, A270 from www.solarpartscomponents.com

What Size is a M8 Bolt?


When it comes to working with bolts, it’s important to have a good understanding of their sizes and dimensions. In this article, we will focus on the M8 bolt, which is a commonly used metric bolt. We will explore the various aspects of its size, including its diameter, length, and thread pitch.


The M8 bolt has a diameter of 8 millimeters. This measurement refers to the thickness of the bolt’s shaft. It is important to note that the diameter of the bolt is not the same as the size of the wrench or socket used to tighten or loosen it. The wrench size for an M8 bolt is typically around 13 millimeters.


The length of an M8 bolt can vary depending on the specific application. However, standard lengths typically range from 20 millimeters to 100 millimeters. If you require a longer or shorter bolt, you may need to consult with a supplier or manufacturer to find the appropriate size for your needs.

Thread Pitch

The thread pitch of an M8 bolt refers to the distance between the threads. It is measured in millimeters and indicates how many threads are present per unit of length. The standard thread pitch for an M8 bolt is 1.25 millimeters. This means that for every 1.25 millimeters of bolt length, there is one complete thread.

Common Applications

The M8 bolt is commonly used in a variety of applications. It is often found in machinery, automotive parts, and construction equipment. Its medium size makes it versatile and suitable for various tasks.

Choosing the Right Bolt

When selecting an M8 bolt for your project, it is crucial to consider the specific requirements and demands of the application. Factors such as load capacity, material compatibility, and environmental conditions should be taken into account. If you are unsure about the appropriate size or type of bolt to use, it is recommended to consult with a professional or refer to industry standards and guidelines.

Thread Engagement

Thread engagement refers to the amount of contact between the bolt and the threaded hole it is inserted into. For optimal strength and performance, it is important to ensure sufficient thread engagement. It is generally recommended to have at least one full diameter of thread engagement for secure fastening.

Tightening Torque

When tightening an M8 bolt, it is crucial to apply the appropriate amount of torque. Under-tightening can result in loose connections, while over-tightening can lead to thread damage or bolt failure. It is recommended to consult the manufacturer’s guidelines or industry standards for the recommended torque values for different bolt grades and materials.


The M8 bolt is a commonly used metric bolt with a diameter of 8 millimeters, standard lengths ranging from 20 to 100 millimeters, and a thread pitch of 1.25 millimeters. It is important to choose the right bolt and apply the appropriate torque to ensure safe and secure fastening. Remember to consult with professionals or refer to industry standards for specific applications to ensure the best results.