Our metric hex head bolts, manufactured to DIN 931, DIN 933, ISO 4014, ISO 4017, DIN 960, DIN 961, and JISB 1186 are the workhorse fastener of general engineering. Driven by an external wrench or socket, they deliver dependable clamping in structural, mechanical, and construction assemblies across a full range of strength classes and thread configurations.

Hex Head Bolts – Metric Sizes

What Is a Hex Head Bolt?

A hex head bolt is a threaded fastener with a six-sided head designed to be driven by a spanner, wrench, or socket. It is the most widely used bolt type in engineering because the hexagonal head offers six wrench-engagement faces, allowing high torque to be applied reliably and the bolt to be turned in confined spaces by resetting the wrench every 60 degrees. Hex bolts are paired with a nut or threaded into a tapped hole to create a strong, serviceable joint.

At Metric Specialities we stock both fully threaded hex set screws (DIN 933 / ISO 4017) and part-threaded hex bolts with a plain shank (DIN 931 / ISO 4014). The plain shank of a part-threaded bolt provides an accurate bearing surface and better shear performance in dowelled or reamed holes, while fully threaded bolts maximise thread engagement in tapped components. With strength classes from 8.8 through 12.9 and stainless options, there is a hex bolt for every structural and mechanical requirement.

Key Features and Benefits

• Universal Wrench Drive: The six-sided head works with standard spanners and sockets, allowing high torque and easy servicing anywhere.
• Full or Part Thread: Choose fully threaded set screws for tapped holes or part-threaded bolts with a plain shank for shear-loaded, reamed joints.
• Wide Strength Range: Classes 8.8, 10.9, and 12.9 cover general to high-strength structural applications.
• Proven Reliability: The most standardised, widely available bolt type, ensuring easy sourcing and replacement.
• Corrosion Options: Zinc-plated, hot-dip galvanised, and stainless finishes suit indoor to marine environments.

Materials and Finishes

• Carbon Steel Class 8.8 (Zinc Plated): The standard general-engineering grade for structural and mechanical work.
• Alloy Steel Class 10.9 / 12.9: High-strength grades for heavily loaded and safety-critical joints.
• Stainless Steel A2 / A4: Corrosion-resistant grades for outdoor, marine, and hygienic use.
• Hot-Dip Galvanised: Heavy-duty corrosion protection for outdoor structural steel.

Standards Compliance

• DIN 931 / ISO 4014 — Hexagon head bolts, coarse thread, part thread.
• DIN 933 / ISO 4017 — Hexagon head set screws, coarse thread, full thread.
• DIN 960 / ISO 8765 — Hexagon head bolts, fine pitch thread, part thread.
• DIN 961 / ISO 8676 — Hexagon head set screws, fine pitch thread, full thread.
• JIS B 1186 — High-strength hexagon bolt, nut, and washer sets for friction grip joints (where supplied as structural sets).
• ISO 898-1 — Mechanical property classes for steel bolts.

Common Applications and Industries

Hex head bolts are the universal fastener of construction, structural steel, and general engineering. They join beams, brackets, base plates, and frames, and appear in machinery, vehicles, agricultural equipment, and infrastructure of every kind. Part-threaded bolts (DIN 931) are chosen where a plain shank must bear shear load in a reamed hole, such as flanged shaft couplings and structural connections, while fully threaded set screws (DIN 933) maximise engagement in tapped components.

Because they are the most standardised and widely stocked bolt type, hex head bolts are specified wherever ease of sourcing, servicing, and replacement is important. High-strength Class 10.9 and 12.9 versions handle heavily loaded and safety-critical joints in lifting, mining, and heavy plant, while galvanised and stainless grades serve exposed outdoor and marine structures.

How to Choose the Right Hex Head Bolt

Begin with the thread configuration: choose a fully threaded bolt to maximise engagement in a tapped hole, or a part-threaded bolt when a plain shank is needed as an accurate bearing surface for shear loads. Then set the strength class from the load — 8.8 for general work, 10.9 and 12.9 for demanding or safety-critical joints.

Select the finish for the environment: zinc plating for indoor and light outdoor use, hot-dip galvanising for exposed structural steel, and A2 or A4 stainless for marine and chemical settings. Confirm the diameter, thread (coarse or fine), and length so the bolt develops full clamp load with adequate engagement, and pair it with a matched-grade nut and appropriate washer or locking method.

Size Range and Availability

Available in M3 through M64 in metric coarse and fine thread, in full and part-threaded forms, across zinc-plated and galvanised steel Class 8.8/10.9/12.9 and A2/A4 stainless.

Why Buy From Metric Specialities

As dedicated metric fastener specialists, we hold hex head bolts in the sizes, grades, and finishes that engineers actually need, backed by clear DIN and ISO standard references so you can specify with confidence. Every item is sourced to recognised standards and quality-controlled, giving you consistent thread fit, strength, and corrosion performance across repeat orders.

Whether you need a single item for a repair or bulk quantities for production, our range, technical guidance, and fast dispatch help you find the exact fastener for the job. If you are unsure which size, grade, or finish suits your application, our team can help you match the right product to your load, environment, and standard, so your assemblies are reliable and built to last.

Frequently Asked Questions (FAQs)

1. What is a hex head bolt used for?

Hex head bolts are used across structural, mechanical, and construction assemblies wherever a strong, serviceable, wrench-driven joint is required. They are the most common general-engineering bolt type.

2. What is the difference between DIN 931 and DIN 933?

DIN 931 (ISO 4014) bolts are part-threaded with a plain shank, while DIN 933 (ISO 4017) set screws are fully threaded. Part-thread suits shear-loaded reamed holes; full thread maximises engagement in tapped components.

3. What does Class 8.8, 10.9 and 12.9 mean on a hex bolt?

These are strength classes. The first number relates to tensile strength and the second to the yield-to-tensile ratio — 8.8 is general-purpose, while 10.9 and 12.9 are high-strength grades for demanding joints.

4. Should I use a full or part-threaded hex bolt?

Use a fully threaded bolt for maximum thread engagement in tapped holes, and a part-threaded bolt when you need a plain shank as an accurate bearing surface for shear loads in reamed or dowelled holes.

5. Are hex head bolts available in stainless steel?

Yes. We stock A2 and A4 stainless hex bolts for corrosion-resistant applications, including marine, outdoor, food, and chemical environments.

6. What is the difference between a hex bolt and a hex set screw?

In metric terminology a hex set screw is simply a fully threaded hex head bolt (DIN 933). It should not be confused with a headless grub set screw used for locking components onto shafts.

7. Do hex head bolts need a nut?

Hex bolts can be used with a nut through a clearance hole, or threaded directly into a tapped hole. The choice depends on whether the mating component is threaded.

8. What finishes protect hex bolts from corrosion?

Zinc plating suits indoor and light outdoor use, hot-dip galvanising provides heavy outdoor protection, and A2/A4 stainless grades resist corrosion in marine and chemical environments.

9. What sizes do you stock for hex head bolts?

We stock M3 through M64 in coarse and fine thread, in full and part-threaded forms, across steel Classes 8.8/10.9/12.9 and A2/A4 stainless, with galvanised options.

10. How do I stop a hex bolt from loosening?

Use the correct torque plus a lock washer, nyloc nut, or thread-locking adhesive. In vibration-heavy applications a combination of correct preload and a locking method is most reliable.