The Complete Guide to Hexagonal Bolts and Hex Head Bolt Types

We also supply a range of specialist Hex Head Screws and Bolts for Industrial Purposes

We are proud to supply an impressive range of large hex bolts that are sized to cater to heavy duty industrial, commercial and construction applications.

These large hexagonal bolts are manufactured from the highest quality grades of stainless steel and are typically more difficult to source than those with smaller thread sizes. However, we have developed a resilient supply chain that offers a strong, steady supply and strive to ensure a prompt delivery, even for large and demanding order quantities to our customers located within the UK.

Click here to view our full range of Hex Head Bolts

What are the standard thread types used on Hex Head Bolt Types?

Thread types are the patterns of ridges and grooves that run along the length of hexagonal bolts. They determine how the bolt interacts with the mating hole or nut, and affect the strength, durability, and ease of installation of the fastener. Understanding these thread specifications is crucial when selecting hex bolt types. There are many different thread types available for hex head bolts, but some of the most common are:

For detailed information about the differences between coarse and fine threads, please see our comprehensive guide on metric coarse and fine thread differences.

These are some of the standard thread types used for hex head bolt types, but there are many more variations and specifications that can affect the performance and compatibility of the fastener. Therefore, it is important to check the requirements of your project before selecting a hexagonal bolt.

Frequently Asked Questions About Hex Head Bolt Types

What is the difference between a Bolt and a Set Screw?

Bolts and set screws are two types of fasteners that are commonly used in various applications. Although they may look similar, there are some key differences between these fastener types.

A Bolt is a type of fastener that has a partially threaded shank and a head that is usually hexagonal or square. Bolts are usually used to secure items in place, tightening and holding by use of a threaded nut and often a washer. The plain part of the shank varies in length; this makes the bolt slightly stronger than the set screw, as whenever a thread is cut onto a shank, a small amount of metal is removed by the process.

A Set Screw is a type of fastener that has a fully threaded shank. Set Screws are usually fully inserted into the receiving object and are commonly used to connect two objects together. They are usually used with wood, metal, and plastics. Set screws are also referred to as Hex Head Screws or Fully Threaded Bolts.

What do the numbers on the Hex Head Bolts mean?

Metric bolts made of 304 stainless steel are marked on the bolt head with A2. The A2 represents 304 stainless steel but can often be followed by another number which represents the tensile strength, for example A2-70. The tensile strength equals 700 MPa general-purpose stainless steel. The number after the A2 will vary depending on the tensile strength of the bolt.

Metric bolts made of 316 stainless steel are marked on the head of the bolt with A4. The A4 represents 316 stainless steel but can often be followed by another number which represents the tensile strength, for example A4-70. The tensile strength equals 700 MPa marine grade stainless steel. The number after the A4 will vary depending on the tensile strength of the bolt.

Common metric classes are 5.8 Low Carbon Steel, 8.8 Medium Carbon Steel, 10.9 Alloy Steel, and 12.9 Alloy Steel. The higher the numbers are, the stronger the material of the fastener is. The number that appears before the decimal, when multiplied by 100, will provide the approximate minimum tensile strength of the bolt. The number after the decimal, when multiplied by 10, will provide the approximate yield strength percentage in relation to the minimum tensile strength. These steels are often quenched and tempered.

How do I choose the right hex bolt type for my application?

Selecting the correct hex head bolt type depends on several critical factors. First, consider the load requirements - for heavy-duty applications requiring maximum strength, choose Grade 8 or 10.9 hex bolts. For general purposes, Grade 5 or 8.8 bolts provide excellent performance. Environmental conditions are equally important; marine or outdoor applications require stainless steel or hot-dip galvanised hex bolt types for corrosion resistance. Thread configuration matters too - fully threaded hexagonal bolts distribute load evenly and are ideal for through-holes, whilst partially threaded bolts offer greater shear strength for structural applications.

What's the difference between hex bolts and hex cap screws?

While often confused, hex bolts and hex cap screws are distinct fastener types with different applications. Hex bolts are designed to be used with nuts and typically have a plain underside to the head. They're commonly used in construction where dimensional tolerances are less critical. Hex cap screws, conversely, feature a washer face (bearing surface) under the head and a chamfered point. They're designed to thread into pre-tapped holes and are used in precision applications where tight tolerances are essential. Hex cap screws generally have better dimensional accuracy and surface finish compared to standard hex bolts.

Why won't my hex bolt tighten properly?

Several factors can prevent proper tightening of hex head bolt types. Cross-threading occurs when the bolt isn't aligned correctly with the nut or tapped hole - always start threading by hand to ensure proper engagement. Worn or damaged threads on either the bolt or mating component will prevent proper tightening. Using the wrong thread pitch (coarse vs fine) is another common issue. Material compatibility problems, such as different thermal expansion rates, can cause loosening. Finally, insufficient lubrication or corrosion can increase friction, making proper torque application difficult. Always ensure you're using the correct fastener type for your specific application and follow recommended torque specifications.