Types of Washers: Functions, Materials & Applications

What Do Washers Do? It’s Key Functions

Washers are not just spacers; they serve multiple mechanical and structural functions. Their key roles include:

• Load distribution: Flat washers spread the compressive force of a bolt or nut over a larger area, preventing damage to softer base materials.
• Surface protection: They act as a barrier between the fastener head and the workpiece, minimising wear or galling on softer materials.
• Shock and vibration absorption: Spring, wave and lock washers provide a spring force that absorbs vibration and prevents joint loosening.
• Preventing loosening: Locking washers (split or toothed) generate friction or mechanical interference to resist rotation and maintain clamp force.
• Enhancing corrosion resistance: Washers made from corrosion-resistant alloys act as sacrificial or protective layers between the fastener and the workpiece.
• Spacing/preloading: Some washers function as shims or spacers, maintaining proper alignment or preload in assemblies.

These functions highlight why engineers must consider both the design and the material of washers when specifying fasteners.

Types of Washers: A Complete Guide

When considering the types of washers for bolts, it’s essential to understand the primary categories. Each of these different types of washers serves a unique purpose in mechanical and structural assemblies.

Flat (Plain) Washers

Flat washers are simple rings used to spread the load of a screw or bolt. They prevent damage when the hole is larger than the fastener and provide a smooth bearing surface for the nut or bolt head. They are ubiquitous in general engineering, furniture assembly and machinery.

Spring Washers

Spring washers are helical or conical components designed to maintain tension. When a bolt loosens due to vibration or thermal cycling, the spring washer compensates for any gap, restoring clamp force. Types include:

• Belleville (conical) washers: conical discs that generate large axial force in a compact size; can be stacked in parallel or series to tune the spring rate.
• Wave washers: have a wave-shaped profile that offers moderate spring force and excellent shock absorption.
• Dome, finger and crescent washers: specialised forms used when space is limited or controlled deflection is required.

Spring washers are common in automotive, aerospace and high-vibration machinery.

Lock Washers

Lock washers prevent fasteners from loosening under vibration. The main varieties are:

• Split lock washers: helical rings split at one point; the cut ends apply spring force and bite into the mating surfaces to maintain friction.
• External and internal tooth (star) washers: washers with serrated teeth that dig into the surface; external teeth provide greater holding power while internal teeth are used where appearance is important.
• Combination and wedge-lock washers: multi-piece systems with wedge surfaces that increase clamping force when loosening is attempted.

These washers find use in electrical assemblies, automotive components and machinery where joint integrity is critical.

Fender Washers

Fender washers (sometimes called penny washers) are flat washers with a very large outside diameter relative to the hole. The larger bearing surface distributes loads over thin or soft materials such as sheet metal and prevents pull-through. They are often used in automotive body panels, HVAC ducting and wooden structures.

Sealing Washers

Sealing washers incorporate a gasket or elastomer bonded to the metal washer. They form a leak-proof connection that prevents the ingress of fluids or contaminants and allow for occasional disassembly. Sealing washers are common in plumbing, hydraulic systems and electronics enclosures.

Countersunk (Finishing) Washers

Countersunk or finishing washers are dished washers used with countersunk screws to provide a flush, decorative finish. They conform to the screw head, spreading the load and concealing the screw head in cabinetry, furniture and architectural fittings.

Shoulder (Insulating) Washers

Also known as shoulder or insulating bushings, these washers have a raised cylindrical portion that fits into the mounting hole. The shoulder isolates the fastener from the substrate and creates a gap, providing electrical or thermal insulation. They are made of non-conductive materials like plastic or ceramic and are essential in electronics.

Wave Washers

Wave washers feature a wave-like shape that produces a spring effect. They offer moderate spring rates, absorb vibration and compensate for manufacturing tolerances in assemblies. These washers are used in automotive transmissions, electrical contacts and small motors.

C-Washers

C-washers (or slotted washers) have a slot cut from the inner hole to the outer edge. This design allows them to be inserted or removed without fully disassembling the bolt; they slide in from the side and are useful in applications requiring frequent adjustment.

Materials Used for Different Types of Washers

1. Common Industrial Metals

2. High-Performance Alloys

3. Nickel-Based Alloys

4. Specialty Materials

Washer Applications Across Industries

Washers may seem like small, simple components but their role is critical in ensuring the reliability, safety and performance of assemblies. Below are some key sectors and the specialized washer applications they rely on:

• Automotive: Flat and lock washers secure engine components, braking systems and suspension assemblies. Spring and wave washers absorb vibration in transmissions and clutches.
• Oil & Gas: Duplex and super duplex stainless washers resist corrosive fluids and high pressures in offshore rigs and pipelines.
• Construction: Structural washers made from carbon or alloy steel provide high strength and are used with A325/A490 bolts in bridges, buildings and wind turbines.
• Marine & Shipbuilding: 316 stainless, titanium and cupro-nickel washers resist saltwater corrosion, while Monel washers withstand high velocity seawater.
• Electrical & Electronics: Shoulder/insulating washers prevent electrical contact and provide thermal isolation.
• Aerospace: Lightweight titanium and Inconel washers deliver high strength at elevated temperatures.
• Chemical Processing: Alloy 20 and Hastelloy washers offer resistance to acids and chlorides.

How to Choose the Right Washer?

Selecting the right component involves more than just picking a size. To choose correctly, engineers and procurement specialists must understand the types of washers and their uses by following these steps:

• Determine the type of load: For static loads, flat washers are suitable; for dynamic or high-vibration loads, choose spring or lock washers.
• Consider the environment: Corrosive or marine environments favour stainless (316), duplex, Inconel, Hastelloy, Monel or cupro-nickel. High-temperature applications may require Inconel or titanium, while clean, dry environments can use carbon or alloy steel.
• Evaluate vibration levels: Use lock washers (split or toothed) or wave and Belleville washers when vibration could loosen the joint.
• Match the fastener and component: The washer’s inner diameter must fit the bolt, and its outer diameter and thickness should suit the bearing surface and load. Use larger OD washers (fender) for soft materials or oversized holes.
• Check material standards: Follow relevant standards (ISO, ASTM, DIN). For structural applications, hardened steel washers (ASTM F436) may be required.

Why Choose Unifit Fastener as your Washer Solution?

• Extensive Range of Materials: We can supply washers in an extensive range of materials, unique steels, and exotic alloy materials such as Inconel, Hastelloy, Monel, and titanium.
• Manufactured to Tighter Tolerances: Washers are typically manufactured in batches and produced to tight tolerances, ensuring excellent fit across applications.
• ISO and Industry Certifications: We are ISO 9001 certified and adhere to the strictest industry standards. We conduct extensive testing and provide full traceability by batch for guaranteed certified quality.
• Global Supply and OEM Support: Established logistics enable high-volume OEM orders worldwide, backed by sector experience across automotive, construction, oil & gas, and aerospace.
• Custom Design & Quantity Flexibility: Our engineers can design and manufacture washers to your specifications—beyond standard shapes, sizes, materials or quantities.

Conclusion: Selecting the Ideal Washer for Your Application

Though small in size, washers can have a major impact on joint reliability. By understanding types, uses, and material properties—and considering load, environment and vibration—engineers can specify washers that deliver durability and safety. Whether you need corrosion-resistant washers for marine projects, high-strength structural washers for construction, or insulating washers for electronics, Unifit Metalloys offers a broad selection and technical expertise to help you get what you need. For expert assistance, reach out to Unifit Fastener for high-quality solutions ready for application.

Flat Washers, Spring Washers, Lock Washers, Fender Washers, Sealing Washers, Countersunk Washers, Shoulder/Insulating Washers, Wave Washers, C-Washers Manufacturer & Supplier in India. Stainless Steel 304/316 Washers, Duplex & Super Duplex Washers, Alloy 20 Washers, Inconel & Hastelloy Washers, Monel Washers, Titanium Washers, Cupro-Nickel Washers, Nickel Washers. OEM & Exporter – Unifit Fastener, Mumbai, India.