Choosing the right fastener may seem like a small decision, but it can have a major impact on the strength, reliability, safety, and lifespan of an assembly. With so many bolts, screws, nuts, rivets, materials, finishes, sizes, and grades available, how do you know which fastener is right for the job?
The best fastener depends on several factors, including the materials being joined, the amount and direction of the load, whether the connection needs to be removable, and the environment in which the fastener will be used.
This practical guide answers some of the most common questions about choosing fasteners and explains what businesses should consider before making a selection.
What Is the Difference Between a Bolt and a Screw?
The primary difference is how the fastener creates and maintains the connection. A bolt is generally used with a nut or a threaded component, while a screw typically engages directly with threads in the material or creates its own threads as it is installed.
Bolts are commonly used when a strong, removable connection is required and both sides of the assembly are accessible. Screws are often preferred when installation needs to be faster, space is limited, or access is available from only one side.
However, terminology can vary by industry and application, so fastener selection should be based on the specific design requirements rather than the name alone.
When Should You Use a Bolt Instead of a Screw?
A bolt is often the better choice when the application requires a strong clamping force, a removable connection, or the ability to service the assembly later.
Bolted connections are frequently used in machinery, equipment, structural assemblies, automotive applications, and other situations where components may eventually need to be disassembled.
Bolts are available in different diameters, lengths, thread configurations, materials, finishes, and strength grades. Choosing the correct combination is important because a bolt that physically fits an assembly is not necessarily strong enough or appropriate for the application.
When Should You Use a Screw?
Screws are a good choice when a fastener needs to engage directly with the material or when using a separate nut would be impractical.
Different screw designs are made for different materials and purposes. For example, some screws are designed to create threads in metal, while others are intended for wood, plastics, sheet metal, or pre-threaded components.
The correct screw should be selected based on the material being fastened, required holding strength, installation method, head style, drive type, thread design, and environmental conditions.
When Are Rivets a Better Choice Than Screws or Bolts?
Rivets are particularly useful when a permanent or semi-permanent connection is desired, especially when access to the back side of an assembly is limited.
Blind rivets, for example, can be installed from one side of a workpiece. This makes them useful for sheet metal, enclosures, equipment, transportation applications, and assemblies where reaching both sides would be difficult or impossible.
Rivets can also provide a consistent, efficient fastening method in production environments. The correct rivet type, diameter, grip range, and material should be matched to the materials and thicknesses being joined.
What Fasteners Are Best for Outdoor Applications?
Outdoor fasteners should be selected with corrosion resistance as a major consideration. Exposure to moisture, humidity, temperature changes, chemicals, and salt can cause unsuitable fasteners to corrode and eventually weaken.
Stainless steel is commonly considered for applications requiring corrosion resistance, while various plated and coated fasteners can provide protection in other environments. The best option depends on the severity of the exposure and the materials being joined.
For coastal, marine, industrial, or chemically aggressive environments, corrosion resistance becomes even more important. Material compatibility should also be evaluated because contact between dissimilar metals can contribute to galvanic corrosion under certain conditions.
What Fastener Materials Resist Corrosion?
Several fastener materials and finishes can provide corrosion resistance, but there is no single option that is best for every environment.
Common choices include:
- Stainless steel: Frequently used where moisture and corrosion resistance are concerns.
- Zinc-plated steel: Provides a protective zinc coating and is commonly used in many general-purpose applications.
- Galvanized steel: Uses a heavier zinc coating and may be appropriate for certain outdoor applications.
- Specialty coatings and finishes: Can provide additional protection for specific industrial environments and performance requirements.
When corrosion is a concern, consider not only the fastener but also the environment, expected service life, base materials, chemicals present, and maintenance requirements.
How Do You Determine the Correct Fastener Size?
Fastener size should be determined by the materials being joined, material thickness, required engagement, load, hole dimensions, and applicable engineering requirements.
Simply choosing the largest fastener that fits is not necessarily the correct approach.
Important dimensions can include:
- Fastener diameter
- Overall length
- Thread pitch or threads per inch
- Thread engagement
- Grip range for certain rivets
- Head dimensions
- Clearance and hole size
For engineered or safety-critical applications, fastener dimensions and specifications should always conform to the requirements of the design.
What Does Fastener Grade Mean?
A fastener grade identifies important mechanical properties of a fastener, including its strength characteristics. Different grading and property-class systems may be used depending on the type of fastener and whether it follows inch or metric standards.
Fastener grade matters because two bolts of the same diameter and length can have very different mechanical properties.
Substituting a lower-strength fastener for one specified by an engineer or equipment manufacturer can create a serious weakness in an assembly. At the same time, using a higher-strength fastener without considering the entire joint is not automatically an improvement.
The fastener, mating components, torque requirements, load, and overall joint design should work together as a system.
When Should You Use Stainless Steel Fasteners?
Stainless steel fasteners are commonly selected when corrosion resistance, appearance, cleanliness, or long service life is important.
They may be appropriate for outdoor equipment, food-related equipment, architectural applications, humid environments, and many other uses where ordinary steel could corrode prematurely.
Not all stainless steel is the same, however. Different stainless alloys provide different levels of corrosion resistance and mechanical performance. The operating environment and application requirements should determine the appropriate material.
How Do I Choose Between a Bolt, Screw, and Rivet?
The following quick-reference table provides a starting point:
| Application Need | Fastener to Consider | Key Consideration |
|---|---|---|
| Strong removable joint | Bolt and nut | Strength, grade, torque and access to both sides |
| Direct fastening into material | Screw | Material, thread design and holding strength |
| Permanent connection | Rivet | Diameter, grip range and material |
| Access from only one side | Blind rivet or appropriate screw | Material thickness and required strength |
| Outdoor installation | Corrosion-resistant fastener | Moisture, salt, chemicals and material compatibility |
| Heavy-duty equipment | Specified bolt or engineered fastener | Load, strength grade and design specifications |
| Assembly requiring future maintenance | Bolt or screw | Ease of removal and repeated service |
This table provides general guidance only. Engineering requirements and manufacturer specifications should take precedence for specific applications.
What Happens If You Choose the Wrong Fastener?
Using the wrong fastener can lead to more than an inconvenient repair. Depending on the application, an incorrect fastener can contribute to premature corrosion, stripped threads, loosening, deformation, broken fasteners, damaged components, or joint failure.
Businesses can also incur significant indirect costs from a poor fastener choice, including equipment downtime, additional labor, replacement parts, warranty claims, and production delays.
That is why fastener selection should be considered part of the overall design and maintenance process rather than simply a purchasing decision.
What Information Should You Have Before Ordering Fasteners?
Before sourcing a fastener, gather as much information about the application as possible. Important questions include:
- What materials are being joined?
- How thick are those materials?
- What loads will the connection experience?
- Will the fastener be exposed to moisture, salt, chemicals, heat, or other environmental conditions?
- Does the connection need to be removable?
- Can installers access both sides of the assembly?
- Is a specific material, grade, finish, standard, or specification required?
- What installation tools will be used?
- Are there space or clearance restrictions?
- Is the fastener part of a safety-critical or engineered assembly?
Providing these details to a knowledgeable fastener supplier can make it much easier to identify appropriate options.
Where Can Businesses Buy Specialty and Industrial Fasteners?
Businesses should work with a fastener supplier that can help them source products based on the actual requirements of their application rather than simply matching a part description.
Allied Bolt & Screw supplies fasteners and related products for a wide range of commercial and industrial needs. Whether your business needs bolts, screws, nuts, rivets, specialty fasteners, or related products, having an experienced supplier can simplify sourcing and help ensure you are ordering the correct product for the job.
Frequently Asked Questions About Choosing Fasteners
What is the strongest type of fastener?
There is no single strongest fastener for every application. Strength depends on the fastener type, diameter, material, grade or property class, joint design, load direction, and installation. The appropriate fastener is the one that meets the engineering requirements of the specific connection.
Are stainless steel fasteners always better?
No. Stainless steel offers valuable corrosion resistance, but it is not automatically the best choice for every application. Strength requirements, temperature, cost, environmental exposure, and compatibility with other materials should also be considered.
Can I replace a bolt with another bolt of the same size?
Not necessarily. Two bolts can have the same dimensions while having different materials, grades, finishes, thread specifications, and strength characteristics. Match the complete specification rather than size alone.
Should I use a rivet or a screw for sheet metal?
Either may be appropriate. Rivets can be an excellent choice for permanent connections and situations where only one side is accessible. Screws may be preferable when the assembly needs to be removed later. Material thickness, load, vibration, and installation requirements should also be considered.
What is the best fastener for outdoor use?
The best outdoor fastener depends on the environment. Stainless steel, galvanized steel, and appropriately coated fasteners are common options. Exposure to moisture, salt, chemicals, and dissimilar metals should be evaluated before choosing a material or finish.
Get the Right Fastener for the Job
The right fastener is not simply one that fits. It should provide the required strength, work properly with the materials being joined, withstand the operating environment, and support the expected service life of the assembly.
When there are questions about size, material, finish, grade, thread type, or fastener style, working with an experienced supplier can help narrow down the options and avoid costly mistakes.
Contact Allied Bolt & Screw to discuss your fastener and industrial supply requirements and find the right products for your application.
