Introducción

If you buy bolts, nuts, screws, washers, anchors, or threaded rods for a project, you already know one thing: a fastener is never “just a small part.” Choosing the wrong fastener can lead to installation delays, corrosion problems, strength failure, or mismatched assembly on site.

This guide explains the basic definition, classification, common materials, standards, surface treatments, and selection logic of fasteners. It is written for procurement teams, distributors, contractors, and industrial buyers who need a clear and practical understanding before placing an order.

Contenido principal

What Is a Fastener?

A fastener is a mechanical component used to connect, fix, secure, or position two or more parts together. In industrial applications, fasteners are widely used in steel structures, machinery, construction, automotive, energy projects, electrical equipment, furniture, and many other assemblies.

Common fasteners include:

• Pernos
• Tornillos
• Nueces
• Lavadoras
• Stud bolts
• Threaded rods
• Anclas
• Alfileres
• Remaches
• Clips and retaining rings

The main purpose of a fastener is to create a reliable joint. Depending on the design, the joint may be removable, semi-permanent, or permanent.

For example, a hex bolt with a nut can usually be removed and replaced. A rivet, once installed, is normally considered a permanent fastening solution. This difference matters when buyers need to consider maintenance, repair, replacement, or future disassembly.

Main Functions of Fasteners

Fasteners are used for more than simply “holding parts together.” In real projects, they usually perform one or more of the following functions.

1. Clamping and Connecting

Bolts, nuts, and washers are used to clamp components together. This is common in steel structures, machinery frames, flanges, brackets, and equipment bases.

2. Positioning

Pins, dowel pins, and some special screws help position parts accurately before or during assembly.

3. Load Transfer

In structural applications, bolts and anchors may transfer tension, shear, or combined loads. This is why strength grade, thread engagement, and installation method must be carefully checked.

4. Anti-Loosening

Lock nuts, spring washers, nylon insert nuts, thread-locking coatings, and special washers are used when vibration or movement may loosen the assembly.

5. Fixing to Concrete or Masonry

Anchors, expansion bolts, wedge anchors, sleeve anchors, and chemical anchors are designed for fixing equipment, rails, brackets, or structures to concrete or masonry bases.

Common Fastener Classifications

Fasteners can be classified in several ways. For buyers, the most useful classification is by product type, thread type, material, strength grade, standard, and surface treatment.

Classification by Product Type

Pernos

Bolts are usually used with nuts or threaded holes. Common types include hex bolts, carriage bolts, flange bolts, socket head cap screws, eye bolts, U-bolts, and T-bolts.

Hex bolts are commonly used in general machinery, construction, and steel structures. Socket head bolts are often selected where space is limited or a cleaner appearance is required.

You can browse more standard fastener types on our fastener products page.

Tornillos

Screws are often designed to be driven directly into materials or pre-tapped holes. Common types include machine screws, self-tapping screws, self-drilling screws, wood screws, drywall screws, and set screws.

A common mistake is treating screws and bolts as the same product. In many purchasing cases, the difference affects thread design, head type, installation method, and application.

Nueces

Nuts are internally threaded fasteners used together with bolts, threaded rods, or studs. Common types include hex nuts, flange nuts, lock nuts, cap nuts, square nuts, and weld nuts.

For high-strength assemblies, the nut grade must match the bolt grade. For example, using a low-grade nut with a high-strength bolt may weaken the entire joint.

Lavadoras

Washers distribute load, protect the surface, adjust spacing, or reduce loosening risk. Common types include flat washers, spring washers, fender washers, square washers, and structural washers.

Washers are often ignored in procurement, but they can affect clamping force, surface protection, and installation stability.

Stud Bolts and Threaded Rods

Stud bolts and threaded rods are widely used in flanges, pipelines, heavy equipment, and construction. A stud bolt may have threads on both ends, while a threaded rod is usually threaded along its full length.

For these products, buyers should confirm diameter, thread pitch, total length, thread length, material, grade, and surface treatment.

Anclas

Anchors are used to fix components into concrete, brick, or other base materials. Common types include wedge anchors, sleeve anchors, drop-in anchors, expansion anchors, and chemical anchors.

Anchor selection depends heavily on base material, load requirement, hole depth, installation condition, and environment.

Classification by Thread Type

Thread is one of the most important details in fastener selection. Even if the diameter looks correct, the fastener may not fit if the thread pitch or thread standard is wrong.

Metric Thread

Metric threads are commonly used in many international markets. Sizes are usually written as M6, M8, M10, M12, M16, and so on. For example, M12 × 1.75 means a 12 mm nominal diameter with a 1.75 mm thread pitch.

UNC and UNF Thread

UNC and UNF are inch-based thread systems commonly used in American standard fasteners. UNC means Unified National Coarse, while UNF means Unified National Fine.

UNC threads are generally more common for general assembly. UNF threads have finer pitch and may be used where stronger thread engagement or more precise adjustment is required.

Coarse Thread vs Fine Thread

Coarse threads are easier to install and more suitable for general applications, especially where the working environment may include dirt, coating thickness, or faster assembly.

Fine threads provide better adjustment and may offer stronger resistance to loosening in some conditions, but they are easier to damage if handled incorrectly.

Classification by Material

Material selection affects strength, corrosion resistance, temperature resistance, cost, and service life.

Carbon Steel

Carbon steel is one of the most common fastener materials. It is cost-effective and suitable for general structural and machinery applications. However, it normally needs surface treatment if used in humid or outdoor environments.

Common carbon steel fastener grades include 4.8, 8.8, 10.9, and 12.9 in metric systems.

Stainless Steel

Stainless steel fasteners are selected when corrosion resistance is important. Common grades include 304, 316, A2, and A4.

304 stainless steel is suitable for many indoor and general outdoor environments. 316 stainless steel offers better corrosion resistance, especially in marine, chemical, or high-humidity environments.

However, stainless steel is not automatically stronger than carbon steel. Buyers should check both material grade and mechanical property class.

Alloy Steel

Alloy steel is often used for high-strength bolts, socket screws, and demanding machinery applications. Grade 10.9 and 12.9 fasteners are commonly made from alloy steel with heat treatment.

These fasteners provide high tensile strength, but surface treatment and hydrogen embrittlement risk should be considered, especially after electroplating.

Brass, Aluminum, and Special Materials

Brass is often used in electrical, decorative, or corrosion-sensitive applications. Aluminum fasteners are lightweight but not suitable for all high-load applications.

Special materials may be required for high temperature, chemical resistance, or specific engineering conditions. In such cases, buyers should provide drawings, working environment, and required standards.

For non-standard sizes or special materials, a customized fastener service is usually more reliable than trying to match an unsuitable standard part.

Classification by Strength Grade

Fastener strength grade is not just a label. It directly affects load capacity and safety.

Metric Bolt Grades

Common metric grades include 4.8, 8.8, 10.9, and 12.9.

• Grade 4.8: general low-strength applications
• Grade 8.8: common high-strength industrial use
• Grade 10.9: higher strength machinery and structural applications
• Grade 12.9: high-strength applications, often used for socket head cap screws and demanding machinery assemblies

Higher grade does not always mean better. A very high-strength bolt may be unsuitable if the application needs ductility, corrosion resistance, or special coating compatibility.

Stainless Steel Property Classes

Stainless steel fasteners may be marked as A2-70, A4-70, A4-80, and similar grades. The letter indicates stainless steel group, while the number relates to tensile strength class.

For example, A4-70 is commonly used when better corrosion resistance is required compared with A2-70.

Classification by Standards

Fastener standards define dimensions, tolerances, thread details, mechanical properties, and sometimes testing requirements. Common standards include:

• DIN
• ISO
• ASTM
• ANSI / ASME
• JIS
• BS
• EN
• Reino Unido

For example, a hex bolt may be supplied according to DIN 933, DIN 931, ISO 4017, or ISO 4014 depending on thread length and dimensional requirements.

A buyer should not only write “hex bolt M12 × 50.” It is better to confirm the standard, grade, material, surface treatment, and quantity. Without these details, different suppliers may quote different products that look similar but are not fully interchangeable.

Classification by Surface Treatment

Surface treatment protects the fastener, improves appearance, and sometimes affects friction during installation.

Zinc Plating

Zinc plating is common for indoor or mild outdoor applications. It is cost-effective and available in white zinc, blue-white zinc, yellow zinc, and other finishes.

Hot-Dip Galvanizing

Hot-dip galvanizing provides a thicker zinc layer and is often used for outdoor steel structures, construction, and infrastructure. However, buyers need to consider thread fit because the coating is thicker than electroplating.

Zinc-Aluminum Coating

Zinc-aluminum coating is used when buyers need better corrosion resistance than ordinary zinc plating while still controlling cost. It is often selected for outdoor fasteners, automotive parts, solar mounting systems, and harsh environments.

Black Oxide and Phosphate

Black oxide and phosphate coatings are often used for appearance, light corrosion protection, or improved lubrication. They are not usually the best choice for long-term outdoor corrosion resistance unless combined with oil or other protection.

PTFE and Special Coatings

PTFE coating may be used for chemical resistance, low friction, or special working environments. It is common in some pipeline, flange, and industrial equipment applications.

How to Choose the Right Fastener

A practical selection process should start from the application, not from the price.

Step 1: Confirm the Application

Ask where the fastener will be used. Is it for steel structure, machinery, concrete fixing, vehicle parts, solar mounting, electrical equipment, or furniture?

The application determines the product type, strength, material, and coating.

Step 2: Confirm the Load Requirement

Will the fastener carry tension, shear, vibration, impact, or only light fixing? For load-bearing applications, grade and installation method are critical.

Step 3: Confirm the Environment

Indoor, outdoor, marine, chemical, high temperature, and high-humidity environments require different materials and coatings.

A zinc-plated carbon steel bolt may be fine indoors but may rust quickly in coastal or chemical environments.

Step 4: Confirm the Standard and Dimensions

Always confirm diameter, length, thread pitch, head type, thread length, standard, and tolerance if required.

Por ejemplo:

M12 × 50, DIN 933, Grade 8.8, zinc plated, full thread

This is much clearer than simply saying “M12 bolt.”

Step 5: Confirm Surface Treatment and Packaging

Surface treatment affects corrosion resistance, appearance, and service life. Packaging affects shipping, storage, and installation efficiency.

For export orders, buyers should also confirm carton weight, pallet requirements, labels, marks, and whether mixed packing is acceptable.

What Buyers Often Overlook

Thread Pitch

Many purchasing mistakes happen because thread pitch is not confirmed. M10 coarse thread and M10 fine thread are not interchangeable.

Matching Bolt and Nut Grades

A high-grade bolt with a low-grade nut may not perform as expected. The assembly should be matched.

Coating Thickness and Thread Fit

Hot-dip galvanizing and some thick coatings may affect thread engagement. Oversized tapping or suitable matching nuts may be required.

Real Working Environment

“Outdoor use” is not specific enough. A fastener used in a dry inland area and a fastener used near the sea may need different protection.

Certification and Inspection Requirements

Some projects require material certificates, test reports, or specific inspection standards. These should be confirmed before production, not after shipment.

To learn more about our company and export supply experience, you can visit our Acerca de nosotros.

Common Misunderstandings About Fasteners

Misunderstanding 1: Stainless Steel Means No Rust Forever

Stainless steel has better corrosion resistance, but it can still corrode under certain conditions, especially in chloride-rich, acidic, or poorly ventilated environments.

Misunderstanding 2: Higher Strength Grade Is Always Better

Higher strength may reduce ductility and may not be suitable for all applications. In some environments, corrosion resistance and toughness may be more important than maximum tensile strength.

Misunderstanding 3: All Zinc Coatings Are the Same

Electro zinc plating, hot-dip galvanizing, zinc-aluminum coating, and mechanical galvanizing are different processes. Their coating thickness, corrosion resistance, cost, and suitable applications are not the same.

Misunderstanding 4: Similar Appearance Means Same Standard

Two bolts may look almost identical but have different head dimensions, thread length, tolerance, or mechanical properties.

Practical Procurement Advice

Before sending an inquiry, prepare as much information as possible:

• Product name
• Estándar
• Size
• Thread pitch
• Material
• Strength grade
• Tratamiento de superficie
• Cantidad
• Aplicación
• Drawing or sample photo
• Destination port or delivery address
• Required certificate or inspection report

If you are not sure about the exact standard, provide the application and photo. A professional supplier can help identify the most suitable option.

For project-based or drawing-based fasteners, share drawings early. This reduces quotation errors and avoids delays during production.

If you need help confirming specifications, you can contact us with your product details, drawings, or application requirements.

Puntos clave

1. A fastener is a mechanical part used to connect, fix, position, or secure components, but different fasteners serve very different purposes.
2. Product type, material, strength grade, standard, thread type, and surface treatment must be confirmed before ordering.
3. Higher strength does not always mean better. The right choice depends on load, environment, installation method, and maintenance needs.
4. Surface treatment should be selected according to real working conditions, not only appearance or price.
5. For industrial procurement, clear specifications reduce quotation errors, production delays, and installation problems.

Preguntas frecuentes

1. What is the difference between a bolt and a screw?

A bolt is usually used with a nut or threaded hole to clamp parts together. A screw is often driven directly into a material or pre-threaded hole. In real purchasing, the difference affects head type, thread design, installation method, and application.

2. How do I choose between carbon steel and stainless steel fasteners?

Choose carbon steel when strength and cost control are the main concerns and the environment is not highly corrosive. Choose stainless steel when corrosion resistance is more important, especially in humid, outdoor, marine, or chemical environments.

3. What information should I provide when requesting a fastener quotation?

You should provide product type, size, standard, material, grade, surface treatment, quantity, application, destination, and any certificate requirements. A drawing or photo is very helpful for non-standard products.

4. Is zinc plating suitable for outdoor fasteners?

Zinc plating can be used in mild outdoor environments, but it may not be enough for harsh, marine, or long-term exposed conditions. Hot-dip galvanizing, zinc-aluminum coating, stainless steel, or special coatings may be more suitable.

5. Can standard fasteners be replaced with custom fasteners?

Yes, but only when the custom design meets the required strength, fit, material, and working condition. Custom fasteners should be produced according to drawings or samples and checked carefully before mass production.

Conclusión

Fastener selection should not start with “which one is cheapest?” It should start with the working condition, load requirement, material compatibility, installation method, and service environment.

For simple indoor assembly, standard carbon steel fasteners with zinc plating may be enough. For outdoor structures, solar mounting, machinery, or high-humidity environments, buyers should pay more attention to coating, material, and strength grade. For special equipment or non-standard projects, drawings and custom production are often necessary.

A well-selected fastener helps reduce installation problems, corrosion risk, maintenance cost, and project delays. If you are preparing a new inquiry, confirm the basic details first, then ask your supplier to recommend the most practical and cost-effective solution.