Washers are small yet crucial components in mechanical assemblies, serving various purposes such as distributing loads, preventing damage, and ensuring secure fastening. Understanding their types, materials, and applications is essential for selecting the right washer for your project. This guide explores everything you need to know about washers, including the differences between USS and SAE washers, washer materials, size chart, various types, and their specific functions.
What Are Washers?
Washers are thin plates, typically disk-shaped, with a hole in the center, used primarily to distribute the load of a threaded fastener, such as a bolt or nut. They serve various functions, including acting as spacers, reducing vibration, and preventing damage to surfaces being fastened. Washers can be made from different materials, including metal and plastic, and are essential in ensuring the integrity of fastenings, especially under conditions involving vibration and stress.
USS vs SAE Washers
Here are the key differences between USS (United States Standard) and SAE (Society of Automotive Engineers) washers.
1. Size and Dimensions
Outer Diameter: USS washers generally have a larger outer diameter compared to SAE washers. This makes USS washers more suitable for larger fasteners and applications requiring a more substantial grip.
Thickness: USS washers are thicker than SAE washers, which contributes to their ability to provide a more secure fit and better load distribution.
2. Design Purpose
SAE washers are designed primarily for automotive applications, USS washers were initially developed for use by the United States Navy, and are intended for industrial applications where a more secure fit is necessary, especially in environments subject to vibration.
3. Standard
SAE washers adhere to specific standards set by the Society of Automotive Engineers. USS (United States Standard) washers follow a different set of standards, which results in a difference in size.
4. Applications
SAE washers are best suited for most general applications due to their smaller size and ease of use. USS washers are more appropriate for larger fasteners or situations where vibration is a concern, as they provide a tighter grip and help prevent loosening.
Washer Materials – What Materials Are Washers Made Of?
Washers come in various materials, including metal, plastic, and other types.
Metals for Washers
1. Stainless Steel Washers
Stainless steel washers are engineered from a steel alloy containing chromium, offering exceptional corrosion resistance, durability, and strength. They are particularly effective in environments exposed to moisture, chemicals, or extreme temperatures. This makes them indispensable in industries such as marine, food processing, and aerospace. Additionally, variants like black oxide stainless steel are chemically treated for enhanced aesthetics while retaining their resistance to rust, even in saltwater or high-salt air conditions.
2. Carbon Steel Washers
Carbon steel washers are known for their robustness and affordability. Typically used in structural applications, they are suitable where corrosion resistance is not a primary concern. However, coatings like zinc or chrome are often applied to extend their service life. These washers are widely used in construction and automotive industries for their strength and cost-effectiveness, though they may rust over time when exposed to outdoor elements.
3. Brass Washers
Brass washers, composed of copper and zinc alloys, are celebrated for their corrosion resistance and excellent conductivity. Their aesthetic appeal makes them ideal for decorative applications, while their resistance to water and heat renders them suitable for plumbing and hot water systems. Brass washers are also commonly used in electrical applications where conductivity and corrosion resistance are vital.
4. Aluminum Washers
Lightweight and corrosion-resistant, aluminum washers are widely utilized in aerospace and electronic applications where minimizing weight is critical. Their non-sparking property makes them safe for hazardous environments. Despite their lightness, they provide sufficient strength for low to moderate load-bearing applications.
5. Silicon Bronze Washers
Silicon bronze washers are highly resistant to corrosion, especially in saltwater environments, making them a preferred choice for marine applications. Over time, they develop a patina, adding a natural, aged aesthetic. These washers are ideal for boats and other marine equipment where durability and long-term corrosion resistance are critical.
6. Copper Washers
Copper washers come with good sealing properties, as they create tight seals when compressed. They are highly resistant to corrosion and excel in high-temperature environments. These washers are frequently used in automotive and industrial machinery systems, particularly in applications requiring reliable seals under pressure.
7. Zinc-Coated Washers
Washers with zinc coatings, such as yellow zinc and hot-dip galvanized washers, are designed for enhanced corrosion resistance. Yellow zinc washers provide moderate rust protection and are suitable for extended outdoor use. On the other hand, hot-dip galvanized washers, coated with molten zinc, are highly durable and used in highway infrastructure, guardrails, and lamp posts, where long-term rust resistance is essential.
Non-Metal Materials for Washers
1. Rubber Washers
Rubber washers excel in creating airtight and watertight seals, making them indispensable in plumbing, HVAC systems, and similar applications. Their flexibility allows them to absorb vibrations effectively, thereby protecting connected parts from damage. They are particularly valued for their ability to prevent leaks and maintain tight seals under pressure.
2. Plastic Washers (Nylon, PTFE)
Plastic washers, including those made from nylon and PTFE, are lightweight, non-corrosive, and non-conductive. These properties make them ideal for electrical insulation in electronics, as well as for preventing galvanic corrosion between dissimilar metals. Additionally, their vibration-absorbing capability makes them suitable for low-load applications in automotive and machinery industries.
Types of Washers and Their Uses
1. Split Ring Lock Washers
Split ring lock washers, also known simply as lock washers, are designed with a cut and twisted ring shape that provides tension to prevent fasteners from loosening due to vibration or torque. When tightened, these washers flatten and create pressure against the fastener, maintaining a secure hold. They are typically used in conjunction with flat washers and are ideal for applications requiring resistance to vibration, such as in machinery or automotive assemblies.
2. High Collar Lock Washers
High-collar lock washers have a thicker and more robust design compared to standard lock washers. They provide greater resistance to flattening and are suitable for high-torque applications where extra pressure is needed to keep fasteners secure. These washers are often used in heavy-duty machinery or industrial equipment, ensuring that nuts and bolts remain tight under significant loads.
3. Internal and External Tooth Lock Washers
Tooth lock washers feature serrated edges, either on the inside (internal lock washers) or outside (external lock washers). Internal toothwashers are ideal for applications requiring a clean, finished look, while external toothwashers provide a stronger grip due to their outward-facing serrations. They are commonly used in electrical and mechanical assemblies to prevent frictional loosening of fasteners.
4. EPDM Washers
EPDM washers combine a stainless steel outer layer with an EPDM rubber backing, providing excellent sealing properties. These washers are primarily used in roofing systems to prevent water leakage by creating a tight seal around fasteners. Their snug fit and durability make them ideal for outdoor applications where weather resistance is critical.
5. Cup Finishing Washers
Cup finishing washers have a semi-spherical shape and are designed for use with countersunk screws. They provide a neat, professional appearance by allowing the screw head to sit flush with or below the surface. These washers are available in various materials, including stainless steel and zinc, and are widely used in woodworking, furniture making, and decorative applications.
6. Metric and USS Flat Washers
Flat washers are the most common type, featuring a simple, flat, circular design with a central hole. Metric flat washers have smaller outer diameters compared to USS (United States Standard) flat washers, which are larger and provide better load distribution. Both types are used to spread the load of a fastener, protect surfaces, and compensate for surface irregularities in automotive, construction, and machinery applications.
7. Fender Washers
Fender washers are a type of flat washer with an extra-large outer diameter relative to the inner hole. This design allows them to distribute loads over a larger area, making them ideal for use with soft or brittle materials like wood, fiberglass, or thin sheet metal. They are commonly employed in the automotive, electrical, and construction industries.
8. Countersunk Washers
Countersunk washers are designed to work with countersunk screws, featuring a conical shape that allows the screw head to sit flush with the material’s surface. These washers enhance the finished appearance of a project and reduce protrusions, making them valuable in precision engineering, woodworking, and furniture making.
9. Shoulder Washers
Shoulder washers, also known as insulating bushings, have a cylindrical protrusion (shoulder) extending from one side. This design provides spacing, and electrical insulation, and prevents metal-to-metal contact. They are commonly used in electronics, automotive, and aerospace applications and can withstand high voltage and temperature extremes.
10. C-Washers
C-washers, or open washers, have a C-shaped design with a gap, allowing for easy installation and removal without fully disassembling the fastener. They are ideal for applications requiring frequent maintenance or where access is restricted, such as in industrial machinery or automotive systems.
11. Belleville Washers
A Belleville washer, also known as a conical spring washer, is a type of mechanical component shaped like a shallow cone. It is designed to provide a predictable and consistent spring force when compressed, and is commonly used to absorb shock, maintain tension, compensate for thermal expansion or contraction, and prevent loosening in bolted connections. They are versatile and can be stacked in various configurations to achieve desired load and deflection characteristics, widely applied in industries such as automotive, aerospace, and manufacturing.
12. Dome Spring Washers
Dome washers, also known as domed spring washers or spherical washers, are specialized fasteners designed to distribute load evenly and reduce stress concentrations in bolted assemblies. Their unique dome-shaped design allows them to compensate for surface irregularities, misalignments, or angular discrepancies between connected components. Typically made from materials like stainless steel, carbon steel, or brass, dome washers are used in applications requiring enhanced stability, vibration damping, or secure fastening under dynamic or uneven conditions. Commonly employed in industries such as construction, automotive, and machinery, they help improve the durability and reliability of mechanical connections.
13. Wave Spring Washers
Wave washers, also known as wave springs or wave spring washers, are thin, disc-shaped components designed with a wavy or corrugated structure. They are primarily used to provide a precise load or compensate for dimensional variations in assemblies. These washers are commonly made from materials like spring steel or stainless steel, offering flexibility and resilience. Their unique wave-like design enables them to absorb shock, reduce vibration, and maintain tension in tight spaces where traditional coil springs may not fit. Wave washers are widely used in industries such as automotive, aerospace, and electronics for applications requiring consistent force in compact areas.
14. Finger Spring Washers
Finger spring washers are specialized washers designed with protruding “fingers” or tabs that provide spring-like flexibility. These washers are typically used to maintain tension, absorb shocks, and reduce vibration in assemblies. The fingers allow for uniform load distribution and compensate for thermal expansion or contraction, ensuring a secure fit in dynamic or fluctuating conditions. Commonly utilized in automotive, aerospace, and industrial applications, finger spring washers are ideal for locking components in place, preventing loosening due to movement or stress, and enhancing the overall stability of mechanical systems.
15. Sealing Washers
Sealing washers feature a rubber or neoprene element that provides a watertight or airtight seal around fasteners. These washers are essential in plumbing, HVAC, and automotive applications where leak prevention is critical, ensuring a durable and long-lasting seal even under pressure.
16. Tab Washers
Tab washers are mechanical locking solutions with tabs or notches that physically secure bolts and nuts. They are used in high-vibration environments to prevent loosening and are common in aerospace, heavy machinery, and industrial applications where joint integrity is paramount.
Washer Dimensions
SAE Washer Size Chart
| Size | Inside Diameter (ID) | Outside Diameter (OD) | Thickness (TH) | |||||
| Basic | Plus | Minus | Basic | Plus | Minus | Max | Min | |
| #4 | 0.125 | 0.008 | 0.005 | 0.312 | 0.008 | 0.005 | 0.040 | 0.025 |
| #6 | 0.156 | 0.008 | 0.005 | 0.375 | 0.015 | 0.005 | 0.065 | 0.036 |
| #8 | 0.188 | 0.008 | 0.005 | 0.438 | 0.015 | 0.005 | 0.065 | 0.036 |
| #10 | 0.219 | 0.008 | 0.005 | 0.500 | 0.015 | 0.005 | 0.065 | 0.036 |
| #12 | 0.250 | 0.015 | 0.005 | 0.562 | 0.015 | 0.005 | 0.080 | 0.051 |
| 1/4 | 0.281 | 0.015 | 0.005 | 0.625 | 0.015 | 0.005 | 0.080 | 0.051 |
| 5/16 | 0.344 | 0.015 | 0.005 | 0.688 | 0.015 | 0.007 | 0.080 | 0.051 |
| 3/8 | 0.406 | 0.015 | 0.005 | 0.812 | 0.015 | 0.007 | 0.080 | 0.051 |
| 7/16 | 0.469 | 0.015 | 0.005 | 0.922 | 0.015 | 0.007 | 0.080 | 0.051 |
| 1/2 | 0.531 | 0.015 | 0.005 | 1.062 | 0.030 | 0.007 | 0.121 | 0.074 |
| 9/16 | 0.594 | 0.015 | 0.005 | 1.156 | 0.030 | 0.007 | 0.121 | 0.074 |
| 5/8 | 0.656 | 0.030 | 0.007 | 1.312 | 0.030 | 0.007 | 0.121 | 0.074 |
| 3/4 | 0.812 | 0.030 | 0.007 | 1.469 | 0.030 | 0.007 | 0.160 | 0.108 |
| 7/8 | 0.938 | 0.030 | 0.007 | 1.750 | 0.030 | 0.007 | 0.160 | 0.108 |
| 1 | 1.062 | 0.030 | 0.007 | 2.000 | 0.030 | 0.007 | 0.160 | 0.108 |
| 1 1/8 | 1.250 | 0.030 | 0.007 | 2.250 | 0.030 | 0.007 | 0.160 | 0.108 |
| 1 1/4 | 1.375 | 0.030 | 0.007 | 2.500 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1 3/8 | 1.500 | 0.030 | 0.007 | 2.750 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1 1/2 | 1.625 | 0.030 | 0.007 | 3.000 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1 3/4 | 1.875 | 0.045 | 0.010 | 3.375 | 0.045 | 0.010 | 0.213 | 0.153 |
| 2 | 2.125 | 0.045 | 0.010 | 3.750 | 0.045 | 0.010 | 0.213 | 0.153 |
USS Washer Size Chart
| Size | Inside Diameter (ID) | Outside Diameter (OD) | Thickness (TH) | |||||
| Basic | Plus | Minus | Basic | Plus | Minus | Max | Min | |
| 3/16 | 0.250 | 0.015 | 0.005 | 0.562 | 0.015 | 0.005 | 0.065 | 0.036 |
| 1/4 | 0.312 | 0.015 | 0.005 | 0.734 | 0.015 | 0.007 | 0.080 | 0.051 |
| 5/16 | 0.375 | 0.015 | 0.005 | 0.875 | 0.030 | 0.007 | 0.104 | 0.064 |
| 3/8 | 0.438 | 0.015 | 0.005 | 1.000 | 0.030 | 0.007 | 0.104 | 0.064 |
| 7/16 | 0.500 | 0.015 | 0.005 | 1.250 | 0.030 | 0.007 | 0.104 | 0.064 |
| 1/2 | 0.562 | 0.015 | 0.005 | 1.375 | 0.030 | 0.007 | 0.132 | 0.086 |
| 9/16 | 0.625 | 0.015 | 0.005 | 1.469 | 0.030 | 0.007 | 0.132 | 0.086 |
| 5/8 | 0.688 | 0.030 | 0.007 | 1.750 | 0.030 | 0.007 | 0.160 | 0.108 |
| 3/4 | 0.812 | 0.030 | 0.007 | 2.000 | 0.030 | 0.007 | 0.177 | 0.122 |
| 7/8 | 0.938 | 0.030 | 0.007 | 2.250 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1 | 1.062 | 0.030 | 0.007 | 2.500 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1-1/8 | 1.250 | 0.030 | 0.007 | 2.750 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1-1/4 | 1.375 | 0.030 | 0.007 | 3.000 | 0.030 | 0.007 | 0.192 | 0.136 |
| 1-3/8 | 1.500 | 0.045 | 0.010 | 3.250 | 0.045 | 0.010 | 0.213 | 0.153 |
| 1-1/2 | 1.625 | 0.045 | 0.010 | 3.500 | 0.045 | 0.010 | 0.213 | 0.153 |
| 1-5/8 | 1.750 | 0.045 | 0.010 | 3.750 | 0.045 | 0.010 | 0.213 | 0.153 |
| 1-3/4 | 1.875 | 0.045 | 0.010 | 4.000 | 0.045 | 0.010 | 0.213 | 0.153 |
| 1-7/8 | 2.000 | 0.045 | 0.010 | 4.250 | 0.045 | 0.010 | 0.213 | 0.153 |
| 2 | 2.125 | 0.045 | 0.010 | 4.500 | 0.045 | 0.010 | 0.213 | 0.153 |
| 2-1/4 | 2.375 | 0.045 | 0.010 | 4.750 | 0.045 | 0.010 | 0.248 | 0.193 |
| 2-1/2 | 2.625 | 0.045 | 0.010 | 5.000 | 0.045 | 0.010 | 0.280 | 0.210 |
| 2-3/4 | 2.875 | 0.065 | 0.010 | 5.250 | 0.065 | 0.010 | 0.310 | 0.228 |
| 3 | 3.125 | 0.065 | 0.010 | 5.500 | 0.065 | 0.010 | 0.327 | 0.249 |