Hex Bolt Dimensions

How To Measure Hex Bolts

Here's a concise overview of the 6 key dimensions associated with metric hex bolts. 

Hex bolts are a common type of fastener known for their hexagonal head and threaded body. Widely used across various applications, from construction and automotive to machinery and electronics, it's crucial to have a good grasp of their metric dimensions when selecting the right fastener for a specific task.

1. Diameter (W): The diameter of a hex bolt is typically measured across the outer edges of its threads. Common metric sizes for hex bolts range from small diameters, such as 6 mm, to larger diameters exceeding 25mm. The diameter is a critical factor in determining the bolt's strength and load-carrying capacity.

2. Length (L): The length of a hex bolt is measured from the bottom of the head to the tip of the threaded portion. Hex bolts come in various metric lengths to accommodate different applications, and it's crucial to select a length that allows sufficient engagement with the materials being fastened. We will discuss thread length later in this article.

3. Thread Pitch (P): The thread pitch represents the distance between adjacent threads on the bolt. It is measured in millimetres per thread. Coarse thread pitches are common in larger diameter bolts, while fine thread pitches are used in smaller diameter bolts, providing different levels of holding strength.

4. Head Width (S): The hexagonal head width is the distance across opposite flat sides of the bolt head. This dimension is essential for selecting the appropriate metric wrench or socket size for tightening or loosening the bolt. This dimension is measured from flat side to flat side across the bolt head. The term "across flats" is often used to specify the metric wrench or socket size needed to tighten or loosen the bolt.

5. Head Height (D): The head height is the distance from the bottom of the head to the top, including any washer face if present. It contributes to the overall profile of the bolt and may be a consideration when clearance is limited.

6. Thread Length (T): When determining the length of the threaded section of a metric bolt, it's important to follow specific standards and guidelines. Here's a concise summary to help you understand how this works for each range of thread lengths:

Thread Length of Hex Bolts Under 125mm

For hex bolts up to 125mm in length, the standard thread length is usually 2 times the bolt diameter plus 6mm.

Here are some examples for hex bolts up to 125mm in length:

• M10 hex bolts up to 125mm typically have a thread length of 26mm
• M12 hex bolts up to 125mm typically have a thread length of 30mm
• M16 hex bolts up to 125  typically have a thread length of 38mm
• M20 hex bolts up to 125mm  typically have a thread length of 46mm
• M24 hex bolts  up to 125mm   typically have a thread length of 54mm

Thread Length of Hex Bolts Between 125mm and 200mm

For hex bolts between 125mm and 200mm in length, the thread length is generally 2 times the bolt diameter plus 12mm.

Here are some examples for hex bolts between 125mm and 200mm in length:

• M10 hex bolts between 125mm  and 200mm typically have a thread length of 32mm
• M12 hex bolts between 125mm and 200mm typically have a thread length of 36mm
• M16 hex bolts between 125mm and 200mm  typically have a thread length of 44mm
• M20 hex bolts between 125mm and 200mm  typically have a thread length of 52mm
• M24 hex bolts between 125mm and 200mm   typically have a thread length of 60mm

Thread Length of Hex Bolts Over 200mm

For hex bolts over 200mm in length, the thread length is generally 2 times the bolt diameter plus 25mm.

Here are some examples for hex bolts over 200mm in length:

• M10 hex bolts between 125mm  and 200mm typically have a thread length of 45mm
• M12 hex bolts between 125mm and 200mm typically have a thread length of 49mm
• M16 hex bolts between 125mm and 200mm  typically have a thread length of 57mm
• M20 hex bolts between 125mm and 200mm  typically have a thread length of 65mm
• M24 hex bolts between 125mm and 200mm   typically have a thread length of 73mm

Understanding these metric dimensions of bolts is crucial for selecting hex bolts that meet the specific requirements of projects in the UK market. It ensures proper fit, optimal strength, and reliable fastening in a variety of applications.

Here's a video showing how to measure bolts.

Fixabolt offer a wide selection of hex bolts and we strive to have them in stock at all times.