Types of Fasteners: A Complete Guide for Industrial Applications

Fasteners are part of almost every assembled system, whether it is a small machine or a large piping network in an industrial plant. They may not be the most visible components, but their role is critical. A poor selection can lead to joint failure, leakage, or repeated maintenance issues.

In practice, choosing a fastener involves more than just size or availability. Load conditions matter, but so do temperature exposure, corrosion, and even how easily the joint can be accessed later. 

Since most fasteners are steel-based and available in multiple grades and standards, the number of options can feel overwhelming at first. This guide covers the main types of fasteners, how they function, and where they are typically used.

What is a Fastener?

A fastener is a mechanical device used to join two or more parts together. In most cases, the joint can be dismantled without damaging the connected components. That is one of the main reasons fasteners are preferred in systems that need periodic inspection or replacement.

Fasteners are usually divided into two broad groups.

• Threaded fasteners include bolts, nuts, screws, and studs. These rely on threads to generate clamping force and hold parts together.
• Non-threaded fasteners include rivets, pins, retaining rings, and keys. These work differently. Instead of threads, they depend on deformation or a tight mechanical fit, and in some cases, they are not meant to be removed at all.

Bolts

Bolts are externally threaded fasteners that pass through pre-drilled holes and are secured with a nut. They do not form their own threads, so they depend entirely on matching components and proper tightening.

Common Bolt Types

1. Hex bolts are used almost everywhere. The six-sided head makes them easy to tighten with standard tools, which is why they are used in both structural and general-purpose connections.
2. Stud bolts are threaded rods without a head. You will mostly see them in flange connections, especially in refinery, petrochemical, and power plant setups. Standards such as ASTM A193 or ASTM A320 are typically specified depending on the service temperature.
3. Carriage bolts have a rounded head with a square section underneath. That square portion prevents rotation during tightening, which becomes useful when working with wood or softer materials.
4. Eye bolts include a loop at the head and are used for lifting or rigging. Load rating and installation orientation both matter during selection. 
5. U-bolts are shaped to wrap around pipes or cylindrical sections. They are commonly used in support systems where alignment needs to be maintained over time.
6. Anchor bolts are embedded in concrete. Once installed, they effectively become part of the foundation and are used to hold structural members or equipment in place.
7. Flange bolts have an integrated flange under the head. This helps distribute the load and, in many cases, removes the need for a separate washer.

Nuts

Nuts are internally threaded fasteners used with bolts or studs. The threads must match in diameter and pitch for the joint to perform as intended.

Common Nut Types

1. Hex nuts are the standard choice for most applications. When higher strength is required, heavy hex variants are used instead. In many cases, that small change makes a noticeable difference in load handling.
2. Lock nuts include a nylon insert or similar feature that increases friction. This helps prevent loosening in vibrating conditions, although they are not always suitable for high-temperature environments.
3. Flange nuts have a built-in flange that distributes the load. They also help reduce the chances of loosening, though not to the same extent as dedicated locking mechanisms.
4. Castle nuts are designed with slots that align with a hole in the bolt. A cotter pin is inserted to lock the assembly. It is a simple method, but very reliable, which is why it is still used in safety-critical applications.
5. Wing nuts are meant for hand tightening. They are only used where loads are low and frequent adjustment is required.
6. Cap nuts cover the exposed end of a bolt. This provides protection and also improves the finished appearance, which sometimes matters more than expected.
7. Coupling nuts are longer than standard nuts and are used to connect two threaded rods. Straightforward in function, but important in extension applications.

Screws

Screws are externally threaded fasteners that are driven directly into the material or into a tapped hole. In some cases, they create their own threads during installation. They are often confused with bolts, but the way they engage with the material is different, and that affects how the load is handled.

Common Screw Types

1. Machine screws are used in precision applications. They are typically installed in tapped holes or used with nuts and are available in different head styles depending on the requirement.
2. Self-tapping screws cut threads into the material as they are driven in. This removes the need for pre-tapping, which can save time during installation.
3. Set screws are used to secure components such as gears or pulleys onto a shaft. They are usually headless and sit flush with the surface.
4. Cap screws, often with a socket head, are used where higher strength and a more compact installation are required.
5. Wood screws have a tapered design and coarse threads. This helps them grip properly in wooden materials without splitting the surface.
6. Sheet metal screws are designed for thin metal sections. Their sharp threads allow them to penetrate and hold without additional processing.

Studs

Studs are threaded rods without a head. They are used where space constraints or design requirements make standard bolting less practical.

1. Fully threaded studs are threaded along their entire length and are used with nuts on both ends. They are simple, but effective.
2. Double-end studs have threads on both sides with a plain section in the middle. One end is fixed into a tapped hole, while the other side is used for tightening.
3. Tap-end studs have unequal thread lengths. One end is intended for permanent installation, while the other is used with a nut.

For flange connections, ASTM A193 Grade B7 and Grade B8 are commonly specified depending on temperature and corrosion requirements. In practice, B7 is used far more frequently.

Washers

Washers are thin, flat or shaped discs placed under bolt heads or nuts to improve load distribution and protect the surface.

Common Washer Types

Some common types of washers are provided below.

1. Flat washers provide a smooth bearing surface and help distribute the load. They are simple components, but leaving them out can damage softer materials.
2. Spring washers apply tension and help resist loosening under vibration. Their effectiveness depends on the application, so they are not always a universal solution.
3. Belleville washers are conical in shape and are used where maintaining tension is important, especially under varying loads.
4. Fender washers have a large outer diameter, which makes them suitable for thin or softer materials.
5. Tab washers include a tab that can be bent after tightening. This physically prevents rotation, which makes them useful in certain locking applications.

Other Fastener Types

1. Rivets are permanent fasteners installed by deforming one end. Once in place, they cannot be removed without damage, so they are used where permanent joints are acceptable.
2. Pins are used for alignment or locking. 

• dowel pins for precision alignment
• cotter pins for locking
• clevis pins for pivot connections
• roll pins for light-duty applications.

3. Retaining rings fit into grooves on shafts or inside bores to prevent axial movement. They are small, but critical in assemblies where components must stay in position.

Fastener Materials for Industrial Applications

Material selection depends heavily on the operating environment. Temperature and corrosion are usually the main factors. In most cases, those two alone decide the material.

Material	Key Properties	Common Applications
Carbon Steel (ASTM A307)	Economical, moderate strength	General-purpose, structural
Alloy Steel (ASTM A193 B7)	High strength, heat-treated	Pressure vessels, flanges
SS 304/304L	Good corrosion resistance	Food processing, general chemical
SS 316/316L	Mo addition, better pitting resistance	Marine, pharmaceutical
Inconel fasteners	Extreme temperature resistance	Aerospace, gas turbines
Hastelloy fasteners	Superior acid resistance	Chemical processing
Monel fasteners	Seawater and HF acid resistance	Marine, oil refining
Super duplex fasteners	High strength + corrosion resistance	Offshore, subsea
Titanium	High strength-to-weight ratio	Aerospace, medical

Fastener Standards

Fastener standards define material properties and performance requirements, and they vary depending on the application.

• ASTM A193 and A194 are used for high-temperature or high-pressure service. ASTM A320 applies to low-temperature conditions.
• ASTM A307 covers general-purpose carbon steel fasteners, while ASTM F593 relates to stainless steel fasteners.
• ISO 898 define mechanical properties for metric fasteners made from carbon and alloy steel. 
• ISO 3506 defines the mechanical properties for metric corrosion-resistant stainless steel fasteners types.

How to Select the Right Fastener

Fastener selection depends on several factors.

• The type of load: Tensile and shear loads behave differently, so the fastener must be chosen accordingly.
• Environmental conditions: Temperature, corrosion, and exposure to chemicals also play a major role. In some cases, these factors matter more than strength.
• Assembly requirements: Some joints need to be permanent (rivets), while others must be easy to disassemble (bolt and nut types). Tool access can also become a constraint.
• Standards compliance: This is important, especially in regulated industries. The joint design itself, whether through-bolted or tapped, will also influence the decision.
• Anti-loosening: In applications with vibration, additional locking methods may be required. Not every joint needs it, but ignoring it where necessary can lead to failure.

Frequently Asked Questions

What is the difference between a bolt and a screw?

A bolt is used with a nut and passes through a hole. A screw is driven directly into a material or tapped hole. The difference mainly comes down to how the clamping force is achieved.

Which material is suitable for corrosive environments?

Stainless steel 316L is commonly used for moderate corrosion resistance. For more aggressive conditions, materials such as Hastelloy C276 fasteners or Monel 400 are preferred.

What does ASTM A193 Grade B7 indicate?

It refers to chromium-molybdenum alloy steel stud bolt types with high strength. These are widely used in high-temperature and high-pressure applications.

How can loosening be prevented in vibrating equipment?

Lock nuts, spring washers, and thread-locking compounds are commonly used. In critical applications, mechanical locking methods such as cotter pins are preferred.

Can different fastener materials be combined?

It is possible, but galvanic corrosion must be considered. When dissimilar metals are used together, the less noble material can corrode faster.

Conclusion

Selecting the right fastener affects not just performance but long-term reliability as well. Each type serves a specific purpose, and the choice should be based on load, environment, and applicable standards. For demanding applications, specialised alloys such as Inconel, Hastelloy, Monel, or super duplex stainless steel are often used because they perform better under extreme conditions.