Types of Hex Bolts and How to Choose Them
7 min
- Hex Bolt Types at a Glance
- Partially Threaded Hexagon Head Bolts
- Fully Threaded Hexagon Head Screws
- Fine-Thread Hex Bolts
- Hex Flange Bolts
- Related Fasteners That Are Not Automatically Hex Bolts
- Materials, Property Classes, and Finishes
- How to Choose a Hex Bolt
- Frequently Asked Questions
- How to Choose the Right Hex Bolt
Hex bolts have a six-sided head that fits a wrench or socket. People use them in many joints because the head gives the tool broad contact and easy access. The main differences come from thread length, thread pitch, head form, material, and finish.
The types of hex bolts also vary by standard and job. A partially threaded bolt suits one kind of joint, while a fully threaded hexagon-head screw suits another. You should look at the full joint before you choose a fastener.
Hex Bolt Types at a Glance
The main hex head bolt types include partial-thread bolts, full-thread hexagon-head screws, fine-thread forms, and flange bolts. Some other fasteners also use a hex head, but they do not always fall under the same bolt family.
These different types of hex bolts should not be chosen by head shape alone. Thread form and grip length also matter. The applicable standard gives the exact dimensions for the fastener.
| Type | Main Feature | Common Use |
| Partially threaded hex bolt | Smooth shank below the head | Joints with a clear grip section |
| Fully threaded hexagon-head screw | Thread along most or all of the shank | General clamp joints |
| Fine-thread hex bolt | Smaller thread pitch | Joints that need finer adjustment |
| Hex flange bolt | Built-in flange below the head | Wider load spread |
| Application-specific hex fastener | Special form for a set job | Depends on the design |
Partially Threaded Hexagon Head Bolts
A partially threaded hex bolt has a smooth shank section below the head. The thread starts farther down the body. This smooth part often sits inside the joint where you want the shank to pass through the parts.
The grip length matters with this type. You should choose a bolt so the smooth shank sits through the joint where the design calls for it, including whether it lies in the shear plane. The threaded section then reaches the nut or threaded part with enough engagement.
People often choose a partial thread when the joint design calls for a smooth section across the joined parts. The choice also depends on the grip length, shear load, thread engagement, hole form, and the applicable standard. Do not judge load capacity by thread length alone, and do not assume a partial-thread bolt is always stronger than a fully threaded fastener. Do not assume a longer bolt always gives the right grip. Check both total length and thread length.
Fully Threaded Hexagon Head Screws
A fully threaded hexagon-head screw has thread along most or all of its shank. This form gives you more thread length for a nut or threaded hole. It also gives you more choice when the exact clamp depth varies.
Naming differs between standards and markets. Some suppliers call these fasteners hex bolts, while others use the term hexagon-head screws. There is no need to force one naming rule across every product range.
This difference matters when you compare hex bolt head types in a catalog. Two products might share the same six-sided head but follow different standards. Check the thread length and dimensions instead of relying on the name alone.
Fine-Thread Hex Bolts
Fine-thread hex bolts have a smaller distance between thread peaks than coarse-thread versions. This gives more threads within the same length. The exact pitch depends on the fastener size and standard.
For a single-start thread, the smaller pitch produces less axial movement per turn. Fine threads may be useful where the joint design specifies fine threads, but thread selection should be based on the applicable standard, material, engagement length, and loading conditions rather than adjustment precision alone. Fine threads also need the correct matching nut or threaded hole. A coarse nut will not fit a fine-thread bolt of the same diameter.
Do not choose fine thread only because it looks more precise. The joint design and standard should decide the thread pitch.
Hex Flange Bolts
A hex flange bolt has a broad flange below the head. The flange gives a wider contact area against the surface. Some flange bolts also have serrations below the flange, while others have a smooth face.
The built-in flange may reduce the need for a separate washer in some joints. It does not remove every washer need. Whether a washer is still needed depends on the joint design, surface condition, coating protection requirements, and the applicable standard. Serrated flange bolts need separate evaluation because the serrations affect the mating surface and locking performance.
Among the types of hex bolts, flange bolts stand out because the head and load-spread surface form one piece. You still need to check the flange diameter and surface type before use.
Related Fasteners That Are Not Automatically Hex Bolts
Several fasteners have a hex shape but belong to other families. A structural bolt might have a hex head, but its dimensions and use follow a structural standard. You should not treat every large hex-head fastener as a general hex bolt.
Coach screws also use a hex head in some forms, but they have a screw thread for wood or similar material. Anchor bolts have a different role because they secure parts to concrete or another base.
Socket-head fasteners do not have an external hex head. They use an internal hex recess instead. A hex key turns the fastener from inside the head.
This is why hex bolt head types should be described with care. Head shape gives one clue, but fastener family and standard give the full answer.
Materials, Property Classes, and Finishes
Hex bolts come in several materials and strength classes. Carbon steel is common in many general joints. Stainless steel suits many wet or corrosive areas, but the exact grade still matters.
Property class tells you about mechanical strength for many metric fasteners. You should match the class to the joint requirement rather than choose a stronger class by default. Other parts in the joint also need compatible strength.
Surface finish also affects corrosion resistance and appearance. Zinc-based finishes are common on many steel fasteners. Other finishes serve different environments.
Do not assume every material or finish exists in every size. Check the supplier data for the exact fastener you need.
How to Choose a Hex Bolt
Start with joint design. Check the total thickness of the parts and decide whether you need a smooth grip section. This helps you choose between a partial-thread and full-thread form.
Next, check thread engagement. The nut or threaded hole needs enough thread contact for the joint design. Make sure the nut matches both the thread diameter and pitch.
Look at the washer needs too. Some joints need a washer to spread load or protect the surface. A flange head already gives a wider contact area, but the joint may still call for a separate washer.
Tool access matters as well. A wrench or socket needs enough space around the six-sided head. Check the environment after that. Moisture or contact with another metal can affect material and finish choice.
The best way to compare different types of hex bolts is by joint need, not by appearance. Grip length and thread form often matter more than small visual differences.
Frequently Asked Questions
What is the difference between a hex bolt and a hex cap screw?
The terminology depends on the applicable standard and market. For metric fasteners, ISO 4014 specifies hexagon head bolts, while ISO 4017 specifies hexagon head screws. Check the product standard, dimensions, and thread configuration rather than relying on the name alone.
Full thread or partial thread: which should you use?
Use the form that matches the joint design. Partial thread gives a smooth grip section, while full thread gives more thread along the shank.
Does a flange bolt remove every washer needed?
No. Some joints still need a washer because of the design or standard.
How to Choose the Right Hex Bolt
The types of hex bolts differ in thread length and pitch, while flange forms also change the head contact area. People should check these features before they choose a fastener.
Start with joint thickness and grip length. Then check thread engagement and material. A correct match helps the bolt sit properly and gives the joint the form the design requires.
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