In demanding fields like industrial engineering and large-scale construction the smallest parts often carry the heaviest burden. Mechanical fasteners are essential in these sectors, ensuring structural integrity, safety, and operational reliability. Though it is usually neglected, a crucial engineering decision is the choosing of bolts and nuts or a certain screw. Making the wrong choice could cause catastrophic structural failure, present major safety concerns, cause expensive downtime and inflated maintenance costs.
This comprehensive fastener guide gives engineers procurement managers and maintenance professionals the detailed knowledge to navigate the complex world of industrial fasteners. We will explore the specific types of fasteners their materials protective coatings and the international standards that dictate their use. A solid understanding of these elements is key to optimizing every joint in your system for peak performance longevity and safety. At Jade Special Metals we believe an informed decision is the cornerstone of engineering excellence and this guide is your roadmap to mastering industrial fastening.
What is a Mechanical Fastener?
A mechanical fastener is a hardware component used to join two or more parts. Unlike permanent joining methods such as welding or glue, mechanical fasteners connect components through friction and gripping force. Their main function is generating and maintaining a precise level of tension which clamps parts together and stops them from separating under operational loads. This force is usually created by tightening a threaded fastener causing it to stretch slightly like a powerful spring and create the tension that secures the joint.
Permanent vs. Non-Permanent Fasteners: A Critical Distinction
Fastener types fall into two primary categories based on reusability.
- Permanent Fasteners are designed for one-time installation. Removing them destroys the fastener or damages the components it holds. The rivet is the classic example of a permanent fastener and is essential where absolute vibration resistance is critical like in aircraft structures and bridge construction. Their permanence creates a secure tamper-proof joint.
- Non-Permanent Fasteners are the focus of this guide and include a huge variety of components like screws and bolts, nuts and washers. Their key feature is the ability to be installed and removed multiple times without damaging the fastener or the assembly. This makes them the standard choice for most industrial fasteners used especially where equipment requires regular inspection maintenance or disassembly.
Different Types of Industrial Fasteners
Fasteners are indispensable components in virtually every construction and manufacturing endeavor, providing the critical connections that ensure structural integrity and operational efficiency. A clear understanding of their diverse types and specific functions is fundamental to any robust assembly.
Bolts
Bolts are externally threaded fasteners that pass through unthreaded holes and are secured with a nut. They are designed to handle both tension and shear loads making them essential to structural and mechanical assemblies.
–Hex Bolts / Hex Head Bolts: The six-sided head is a common sight in industry, offering excellent grip for wrenches and sockets for fast installation and removal. These are widely used in structural steel connections, machinery frames, engine blocks, and general industrial fabrication.
–Carriage Bolts: These have a smooth domed head and a square neck directly below it. The square neck bites into softer materials like wood when tightened to prevent the bolt from spinning. This design allows for single-tool installation. You’ll find carriage bolts common in wood-to-metal joints, timber framing, and any application needing a smooth, snag-free exterior.
–Flange Bolts: A smart design featuring a built-in washer or flange at the base of the head. The flange distributes the clamping load over a wider area, which protects the component surface and eliminates the need for a separate washer. They are ideal for automotive frames, high-vibration equipment, and assembly lines where reducing parts speeds up production.
–Stud Bolts / Double End Bolts: A stud is a headless threaded rod, often with threads on both ends. It passes through flanges and is secured with a nut on each side. This setup is crucial for even pressure distribution across gaskets. Stud bolts are vital for high-pressure and high-temperature flange connections in oil and gas pipelines, chemical plants, and power generation facilities.
–Socket Head Screws / Allen Bolts: Though commonly called screws, these high-strength fasteners act as bolts. Their cylindrical head has an internal hex socket driven by an Allen key. This design allows for higher tightening torques and is perfect for use in tight or recessed spots. They are frequently employed in machine tools, robotics, plastic injection molds, and engines where high clamping force is needed in limited space.
Screws
Unlike bolts, screws are made to thread directly into one of the components. They do this by cutting or forming their own mating thread in the material.
–Machine Screws: These have fine uniform threads for use in pre-tapped holes or with a nut. They are generally smaller than most bolts. You’ll often find them securing parts in electrical enclosures, machine guards, electronics, and switchgear.
–Sheet Metal Screws: Their sharp threads and sharp points easily form threads in thin sheet metal. These are commonly used in HVAC ductwork, metal roofing, gutter installation, and assembling metal enclosures.
–Self-Tapping Screws: These screws save significant time by creating their own threads in a pilot hole. A self-drilling screw goes one step further with a drill-bit tip that makes the hole and forms the thread in one action.They are widely applied in metal building construction, automotive assembly, and any high-volume production where efficiency is a priority.
Nuts
A nut is an internally threaded fastener paired with a bolt or stud to create the clamping force that holds a joint together.
–Hex Nuts: The standard partner for hex bolts available in grades and materials to match the bolt’s strength.
–Lock Nuts: Engineered to resist loosening from vibration. A common type is the nylon-insert lock nut which has a nylon collar that grips the bolt threads. Others use distorted threads for a mechanical lock. These are crucial for vehicle suspensions, industrial machinery, and any equipment subject to constant movement.
–Flange Nuts: This nut has an integrated wide flange that works like a washer to distribute pressure and resist loosening.
–Cap Nuts: These have a domed head that covers the end of the bolt. This protects threads from damage and gives a safe finished look.
Washers
Washers are thin discs with numerous uses under a nut or bolt head
–Flat Washers: Their main purpose is to distribute the weight from the fastener across a larger surface to avoid damage particularly on softer materials like aluminum.
–Spring Washers / Lock Washers: These are split and helically shaped. When compressed they push back against the fastener head creating friction that helps prevent loosening from vibration.
Materials Used for Fasteners
The choice of fastener materials is the most important factor determining a fastener’s strength, corrosion resistance and suitability for an application.
Carbon Steel & Alloy Steel Fasteners
This group of steel fasteners is the most common due to its strength and value. Properties are defined by standards like the SAE fastener grades.
–SAE Grade 2: Low-carbon steel for general-purpose low-stress applications.
–SAE Grade 5: Medium-carbon steel heat-treated for more strength. A workhorse for automotive and machinery needs identified by 3 radial lines on the head.
–SAE Grade 8: A heat-treated medium-carbon alloy steel. These high-strength fasteners are used where significant clamping force is required like in heavy equipment and critical joints. Identified by 6 radial lines on the head.
Stainless Steel Fasteners
Known for excellent corrosion resistance, stainless steel fasteners are essential in harsh environments.
–A193 B8 Fasteners: This specification covers fasteners manufactured from Type 304 stainless steel, which offers good general corrosion resistance suitable for a wide range of applications.
–A193 B8M Fasteners: For superior protection against aggressive environments like saltwater and various acids, engineers frequently specify A193 B8M fasteners, made from Type 316 stainless steel. This makes them the preferred choice for critical marine and chemical processing fastener applications.
–ASTM F593 Fasteners: ASTM F593 is a widely recognized specification that defines the requirements for a comprehensive selection of stainless steel bolts and screws engineered for diverse general-purpose fastening applications.
High-Performance Alloy Grades for Extreme Service
The most demanding jobs require specialized alloy steel fasteners governed by ASTM fastener standards.
–A193 B7 Fasteners: This chromium-molybdenum alloy is the standard for high-temperature high-pressure service in the oil and gas industry. It is almost always paired with nuts manufactured to the ASTM A194 Grade 2H specification.
–A193 B16 Fasteners: A chromium-molybdenum-vanadium alloy for even higher temperature bolting than A193 B7 Fastener.
–A320 L7 Fasteners: The low-temperature version of B7 designed to stay tough and resist becoming brittle in cryogenic service down to -150°F.
–A325 Fasteners: These heavy hex structural bolts are made specifically for steel-to-steel connections in buildings and bridges.
–A453 GR.660 Fasteners: A high-strength superalloy that keeps its strength at extreme temperatures for use in gas turbines and jet engines.
Other key nut specifications include ASTM A194 Gr.7 fasteners, ASTM A194 Gr.8 fasteners, and the stainless ASTM A194 Gr.8M fasteners and ASTM F594 fasteners. General-purpose nuts may be covered by ASTM A563 fasteners. Low-carbon bolts for general use are specified as A307 fasteners.
Different Types of Coatings Available
Coatings protect fasteners from corrosion reduce installation friction and improve appearance.
–Zinc Plating: A thin electroplated zinc layer offers basic corrosion resistance for indoor or mild environments.
–Hot-Dip Galvanizing (HDG): Dipping the fastener in molten zinc creates a thick durable coating for excellent long-term protection in outdoor and marine use.
–Phosphate Coating: This coating offers mild corrosion resistance and a porous surface that holds paint and lubricants well.
–PTFE / Teflon Coatings: These fluoropolymer coatings provide outstanding corrosion resistance low friction for consistent torquing and excellent chemical resistance. They are the premium option for corrosion-resistant fasteners in offshore subsea and chemical plant work.
How to Choose Different Types of Fasteners
Choosing the right fastener is a methodical process that directly impacts the performance, safety, and longevity of your application. To ensure you make the optimal selection, ask yourself the following critical questions:
Q. Which fastener type do you require?
Are you looking for a bolt, screw, nut, washer, or a more specialized fastener like a rivet or a self-clinching fastener? Your initial understanding of the basic types will guide your search.
Q. What application requires these fasteners?
Consider the specific function the fastener will perform. Is it for structural integrity, joining thin sheets, allowing frequent disassembly, or preventing loosening due to vibration?
Q. What is your actual need for a fastener?
This expands on the application. Are you primarily concerned with clamping force, shear resistance, corrosion prevention, or a combination of these? Understanding the primary role the fastener plays will narrow down your options.
Q. What are the main properties your manufactured part must include?
This refers to the characteristics of the fastener itself that are crucial for the application. Think about:
–Strength requirements: What load (tension, shear) will it bear? This dictates the material grade (e.g., SAE Grade 5, ASTM A193 B7).
–Corrosion resistance: Will it be exposed to moisture, chemicals, or saltwater? This will lead you to stainless steels or specific coatings.
–Temperature range: Will it operate in extreme heat or cold? This influences material choice (e.g., A320 L7 for low temperature).
–Assembly and maintenance needs: Does it need to be easily installed in tight spaces (socket head screws)? Does it require frequent removal (non-permanent)?
–Specific features: Do you need a wide load distribution (flange bolt/nut), self-tapping capabilities, or vibration resistance (lock nuts)?
Once you have clear answers to these questions, you will be well-equipped to select the perfect threaded fasteners for your use. This systematic approach ensures that you choose fasteners with the appropriate features, leading to the high performance and reliability of your application. Making the correct decision in selecting fasteners is paramount to engineering success.
Conclusion
Fasteners may be small but their impact on industrial performance and safety is huge. A single fastener failure in a critical joint can cause damage that far outweighs its price. By moving past a commodity mindset engineers can build systems that are more reliable, safer and more cost-effective.
A deep understanding of the types of fasteners and how materials, coatings and standards work together is the sign of a true professional. Whether you assemble machinery build infrastructure or maintain high-pressure systems choosing the right fastener is critical. It ensures your assets meet global engineering standards and operate with the integrity they were designed for.
Jade Special Metals offers a wide range of certified fastening solutions, strictly adhering to industry standards. Our large inventory of industrial fasteners from standard carbon steel fasteners to high-performance alloys strictly adheres to ASTM and SAE standards and is ready for the world’s toughest environments.
FAQs
What are the 5 basic types of fasteners?
The five most basic fasteners types are bolts, screws, nuts, washers and rivets. These are the core categories for almost all industrial and commercial assembly.
What are the classifications of fasteners?
Fasteners uses and designs are classified by several key attributes:
- Function: Permanent like rivets or Non-Permanent like bolts and nuts.
- Head Type: Hex socket flange carriage or countersunk.
- Thread Type: Coarse (UNC) Fine (UNF) or Metric.
- Material & Grade: Carbon steel fasteners alloy steel fasteners stainless steel and superalloys with specific fastener grades like SAE Grade 5 or ASTM A193 B7.
What are the different types of PEM fasteners?
PEM® is a brand of self-clinching fasteners pressed into sheet metal to become a permanent part of an assembly. The main types are self-clinching nut studs and standoffs used to add threads to thin metal enclosures.
What are MS fasteners?
MS stands for Military Standard. MS fasteners are made to the strict specifications of the U.S. Department of Defense for use in aerospace defense and other critical sectors where failure is not an option.
Which type of fastener is best?
There is no single best fastener because the choice is always application-dependent. For high-strength high-pressure service A193 B7 fasteners are often best. For marine use corrosion-resistant fasteners like A193 B8M fasteners are superior. The best fastener is the one that correctly meets the load environment and standards for your specific job.
What is the most used fastener?
The hex head bolt and the machine screw are among the most widely used types of fasteners across all industries due to their versatility and cost-effectiveness.
How to choose fastener length?
Measure the total thickness of the materials being joined. Add the height of the nut and any washers. Ensure at least two to three full threads extend past the nut after tightening for a secure joint. For a screw in a tapped hole the thread engagement should be 1 to 1.5 times the fastener’s diameter.
