what are hex bolts

What are Hex Bolts & Hexagon Bolts?

There are many types of bolts and screws that all serve unique purposes. The most common bolt is a hexagon head bolt, called a hex bolt, or even just a bolt. When you hear the word ‘bolt’, a hex bolt is usually what you would think of. Characterised by the hexagonal-shaped head and its threaded shaft, which can either be fully threaded or partially threaded. 

Although used in many instances, the hex bolt is generally used in construction, engineering, and the automobile industry. Although they come in both partial and full-thread variations, partial thread is more commonly used when using this type of bolt as the non-threaded part of the shaft provides extra strength, making it more load-bearing than its fully threaded version, which has its own unique benefits. 

The hex bolt is available in many sizes and materials, including bright zinc plated, stainless steel, and even brass.

What Are Hex Bolts Used For?

The hex bolt is known as a threaded fastener when used with a hexagonal or square nut, making it highly adaptable for many jobs. 

Hex bolts can be used to bind solid materials like metal and wood, especially when used in combination with nuts and washers. The larger the washer, the more stable the joint as more surface area is being covered and therefore the more evenly distributed the weight is.

Washers have several purposes when used with a bolt:

  • To protect the joint from any damage from the fastening process.
  • Distribute load more evenly between the nut and the head of the bolt.
  • Add spacing between the bolt head and the joint to make the bolt ‘longer’.
  • Protect the objects being fastened from vibration damage. They work as a vibration dampener.
  • Create a waterproof seal so liquid cannot get into the join as easily.

The majority of hex bolts are used in engineering and building projects because of their strength and flexibility.

Hex bolts are easy to use because their head shape fits easily into a spanner/wrench or can be loosely tightened by hand. Hexagonal socket bits are commonly found on sites and in workshops so using a hexagon head bolt can make life easier as switching tools during a job can be made less frequent.

Types of Materials Used with Hex Bolts

Steel Bolts: Typically made from steel or stainless steel, hex bolts can be coated in other finishes as well depending on their application. They could be plated in zinc to improve their strength or coloured to match their surroundings. The steel used varies on strength and grades, with anything between grade 5 and grade 8 being the most popular. As a rule of thumb, the higher the number, the stronger the steel and the higher tensile strength it has. 

Stainless Steel Bolts: Hex bolts made in stainless steel are generally used on exterior projects as they are more resistant to rusting. A2 and A4 indicate the levels of chromium used in the stainless steel manufacturing process. 

The most commonly used stainless steel is A2 stainless. This grade is more than adequate for most outdoor projects, particularly in the UK. 

If the bolts are needed for marine projects, A4 stainless steel would be the best option as they have even greater anti-corrosive properties than A2 stainless, so the salt water does not make them corrode for extended periods of time. This is why this grade is more commonly found on boats. A4 stainless steel is generally unnecessary for most outdoor projects and it is more expensive and less readily available in this country.

Bright Zinc Plated: These are steel boats that have been coated with zinc to make them stronger. Although they are stronger, they also have less play in them so for groundworks or projects where structures are likely to move slightly over time, stainless steel can be preferable as it is more flexible before it breaks. BZP hex bolts are bright in colour (hence the name), and can be seen as more aesthetically pleasing in some indoor projects. Their main drawback is they are reasonably prone to rusting, although the zinc plating does offer mild corrosion protection.

Brass Bolts: Brass is more for decoration. They are more expensive and not as strong as steel bolts but they can look great in interior design projects where the bolt heads are exposed.

Self Colour: Best used for internal applications as they have no extra protection against corrosion. The colour changes over time with oxidisation, but usually start off black, or at least, a very dark grey.


Types of Hex Bolts

Size is the main characteristic of the hex bolt. The size of the shaft and the head depend on your needs, but they all conform to a standard set of measurements known as the DIN number. The DIN number for a hexagon bolt is DIN 931. They can be found with a thread diameter of 2mm (M2) right up until 30mm (M30) and more. 

Depending on your application, you can also choose from a range of materials that will best suit your needs. Stainless steel is more resistant to surface rusting, and therefore lasts longer on exterior jobs, but BZP (Bright Zinc Plated) has a higher strength rating, although it can snap more suddenly as they are not flexible, as mentioned. 

Look at the role your hex bolts play then decide which is best suited for your end project. Same goes for threaded and partially threaded bolts.

Fully or Partially Threaded Bolts?

Partially threaded bolts have the screw thread going only part-way up the shaft of the bolt.

This makes the bolt stronger as the bolt shank will not have the grooves carved into it, thus having a greater mass volume and reducing the strain on the bolt.

On exterior work, the partially threaded bar can be cut off once the nut is securely in place, thereby reducing the amount of exposure to water seepage down the shaft of the bolt preventing rusting along the length of the bolt.

M16 fully threaded bolts can be used to bolt together several items as there is more thread to use, and they are also ideal for pre-threaded holes. The downside of this is that the threaded shaft has less strength so holding many heavy items at once will put a lot of strain on the bolt.


Hexagon Bolt Sizes

Hex bolts are displayed in 'M' sizes, which is the diameter of the thread in millimeters. This must not be confused with the diameter of the head, which is a common mistake people make. Generally, the larger the M number the stronger the bolt as there is a greater volume mass, meaning it can be used in heavier applications. As a rough guide, the thread length on partially threaded bolts is three times the width of the bolt.

Where to Buy Hex Bolts

At Fixabolt we stock a wide range of common sized hex bolts. Usually, hex bolts in smaller lengths come fully threaded. Longer bolts, which would generally be used for larger materials, are partially threaded, and therefore stronger. If we do not have the size you are looking for, let us know using a contact form or live chat message and we will do our best to help you find the bolts you need.

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