Washers
What are Washers?
Washers are thin discs with a center hole used under a nut or bolt head to spread load, protect surfaces, support consistent torque, and in some cases seal against fluids or resist loosening.
Do you need washers for screws?
Often yes. Washers help on soft materials and anywhere you want better load spread or surface protection. Some screws have built-in flanges or features that reduce the need, but a simple flat washer is still useful in many installs.
- Soft materials such as wood, plastics, and drywall benefit from a washer under the head
- Enlarged or irregular holes are easier to bridge with a larger outside diameter
- Where vibration is present, choose a lock style or add a separate locking method
What types of washers are there?
- Flat washers for load distribution and surface protection
- Lock washers split or toothed styles that add resistance to rotation
- Fender washers extra large outside diameter to cover big or slotted holes
- Sealing washers metal backed with an elastomer to help prevent leaks
- Conical and cup styles spring action to help maintain preload
- Square and specialty shapes for channels, timber, or specific hardware
What size washer do I need? inch and metric
- Match the nominal washer size to the fastener size such as 1/4 in or M6
- Verify the inner diameter fits the shank without binding
- Choose the outside diameter and thickness for the load you need to spread
- Select standard, wide, or fender patterns based on hole size and clearance
Which washer material should I choose
18-8 and 304 stainless steel
General purpose corrosion resistance with a clean appearance for indoor and light outdoor use.
316 stainless steel
Preferred for marine, salty, or chemically harsh environments; pair with 316 hardware when possible.
Zinc plated steel
Economical for dry interiors with light corrosion protection.
Hot dip galvanized steel
Thick zinc layer for outdoor structural work; match with galvanized bolts and nuts.
Brass and silicon bronze
Conductive and corrosion resistant choices used in electrical and marine applications.
Aluminum
Lightweight with natural corrosion resistance; consider galvanic compatibility in mixed-metal joints.
When should I use a lock washer
Use a lock washer when movement or vibration could loosen the joint. Split and tooth styles add bite. For severe vibration, consider wedge-lock pairs or a liquid threadlocker.
How do I install washers correctly
- Place the washer under the rotating part, either the nut or the bolt head
- Keep bearing surfaces clean and flat for consistent preload
- Avoid over-torque on sealing types to protect the elastomer
- Re-check torque after initial run-in if soft materials compress
Washers vs alternatives what should I know
Washers help with load spread, surface protection, and in some cases sealing or anti-rotation. They do not replace good joint design. For high vibration or safety critical assemblies, add a locking feature or choose hardware designed to resist back-off.
Washer Specifications
AN960C Washer Specifications
| Washer Size | Inner Diameter (ID) | Outer Diameter (OD) | Thickness |
| #2 C2 | 0.099" | 1/4", 0.25" | 1/32", 0.0313" |
| #2 C2L | 0.099" | 1/4", 0.25" | 1/64", 0.015625" (Light) |
| #3 C3 | 0.109" | 1/4", 0.25" | 1/32", 0.21875" |
| #3 C3L | 0.109" | 1/4", 0.25" | 1/64", 0.015625" (Light) |
| #4 C4 | 0.125" | 0.312" | 1/32", 0.03125" |
| #4 C4L | 0.125" | 0.312" | 1/64", 0.015625" (Light) |
| #5 C5 | 0.140" | 0.438" | 3/64", 0.046875" |
| #6 C6 | 0.149" | 0.375" | 1/32", 0.03125" |
| #6 C6L | 0.149" | 0.375" | 1/64", 0.015625" (Light) |
| #8 C8 | 0.174" | 0.375" | 1/32", 0.03125" |
| #8 C8L | 0.174" | 0.375" | 1/64", 0.015625" |
| #10 C10 | 0.203" | 0.437" | 1/16", 0.0625" |
| #10 C10L | 0.203" | 0.437" | 1/32", 0.03125" (Light) |
| 1/4" C416 | 0.265" | 0.500" | 1/16", 0.0625" |
| 1/4" C416L | 0.265" | 0.500" | 1/32", 0.03125" (Light) |
| 5/16" C516 | 0.328" | 0.562" | 1/16", 0.0625" |
| 5/16" C516L | 0.328" | 0.562" | 1/32", 0.03125" (Light) |
| 3/8" C616 | 0.390" | 0.625" | 1/16", 0.0625" |
| 3/8" C616L | 0.390" | 0.625" | 1/32", 0.03125" (Light) |
| 7/16" C716 | 0.453" | 0.750" | 1/16", 0.0625" |
| 7/16" C716L | 0.453" | 0.750" | 1/32", 0.03125" (Light) |
| 1/2" C816 | 0.516" | 0.875" | 1/16", 0.0625" |
| 1/2" C816L | 0.516" | 0.875" | 1/32", 0.03125" (Light) |
| 9/16" C916 | 0.578" | 1.062" | 1/16", 0.0625" |
| 9/16" C916L | 0.578" | 1.062" | 1/32", 0.03125" (Light) |
| 5/8" C1016 | 0.641" | 1.187" | 1/16", 0.0625" |
| 5/8" C1016L | 0.641" | 1.187" | 1/32", 0.03125" (Light) |
| 3/4" C1216 | 0.766" | 1.312" | 3/32", 0.09375" |
| 3/4" C1216L | 0.766" | 1.312" | 1/32", 0.03125" (Light) |
| 7/8" C1416 | 0.890" | 1.500" | 3/32", 0.09375" |
| 1" C1616 | 1.016" | 1.750" | 3/32", 0.09375" |
Stainless Steel Extra Thick Flat Washer Specifications
| Washer Sizes | Inner Diameter (ID) | Outer Diameter (OD) | Thickness |
| 1/4" | 9/32" | 5/8", Max 0.630" - Min 0.5625" | Max 0.125" - Min 0.100" |
| 5/16" | 11/32" | 3/4", Max 0.760" - Min 0.700" | Max 0.125" - Min 0.100" |
| 1/2" | 17/32" | 1-1/4", Max 1.252" - Min 1.248" | Max 0.125" - Min 0.100" |
| 1/2" | 17/32" | 1-1/2", Max 1.500" - Min 1.4375" | Max 0.125" - Min 0.100" |
NAS Washer Specifications
| Washer Size | Inner Diameter (ID) | Outer Diameter (OD) | Thickness |
| #0 | Max 0.063" - Min 0.060" | Max 0.099" - Min 0.090" | Max 0.016" - Min 0.013" |
| #2 | Max 0.089" - Min 0.085" | Max 0.149" - Min 0.140" | Max 0.016" - Min 0.013" |
| #3 | Max 0.102" - Min 0.093" | Max 0.180" - Min 0.150" | Max 0.032" - Min 0.026" |
| #4 | Max 0.115" - Min 0.105" | Max 0.208" - Min 0.200" | Max 0.032" - Min 0.026" |
| #5 | Max 0.128" - Min 0.118" | Max 0.238" - Min 0.228" | Max 0.032" - Min 0.026" |
| #6 | Max 0.143" - Min 0.133" | Max 0.267" - Min 0.257" | Max 0.032" - Min 0.026" |
| #6L | Max 0.143" - Min 0.133" | Max 0.267" - Min 0.257" | Max 0.016" - Min 0.013" (Light) |
| #8 | Max 0.169" - Min 0.160" | Max 0.304" - Min 0.296" | Max 0.032" - Min 0.026" |
| #8L | Max 0.169" - Min 0.160" | Max 0.304" - Min 0.296" | Max 0.016" - Min 0.013" (Light) |
| #10 | Max 0.195" - Min 0.189" | Max 0.354" - Min 0.325" | Max 0.063" - Min 0.058" |
| #10L | Max 0.195" - Min 0.189" | Max 0.354" - Min 0.325" | Max 0.032" - Min 0.028" (Light) |
| #416 | Max 0.255" - Min 0.245" | Max 0.468" - Min 0.458" | Max 0.063" - Min 0.058" |
| #416L | Max 0.255" - Min 0.245" | Max 0.468" - Min 0.458" | Max 0.032" - Min 0.028" (Light) |
FAQs about Washers
This FAQ explains how to choose washer materials and sizes, when to pick flat vs. lock styles, basic installation tips, sealing considerations, and best practices so you can select and install washers with confidence.
Washers distribute load, protect surfaces, and can help prevent fastener loosening. They play a crucial role in creating secure and reliable connections in various applications.
Select a washer with an inner diameter slightly larger than the fastener and an outer diameter appropriate for your application. Consider the load distribution requirements and any space constraints in your project.
While some washers can be reused, it's generally recommended to use new washers, especially in critical applications. Reusing washers may compromise their effectiveness and the overall integrity of the fastened joint.
Fender washers have a larger outer diameter compared to standard flat washers, providing greater load distribution. This makes them ideal for applications where increased bearing surface is needed or when working with softer materials.
Lock washers can help prevent loosening in many applications, but their effectiveness can vary depending on the specific situation. Factors such as vibration, temperature changes, and load type can impact their performance. In critical applications, consider using multiple locking methods or consult with a fastener expert.
A flat washer is a thin, round disc with a central hole, used to distribute load and protect surfaces under a fastener.
A flat washer spreads the load of a fastener, prevents damage to surfaces, and acts as a spacer or shim.
They can reduce mismatch with aluminum parts, but you still need to consider coatings, isolation, and the service environment.
They are flat washers with square outside geometry, typically used in channels or timber where flat sides prevent rotation.
Zinc plated is a thin, economical coating for indoor use; hot-dip galvanized is much thicker for outdoor structural applications.
Tighten evenly until the seal compresses; avoid over-torque that can damage the elastomer or cause leaks.
Yes, but consider galvanic corrosion in wet environments; isolate metals or match coatings when possible.
To cover oversized or slotted holes and to spread load across thin materials due to its large outside diameter.
316 stainless is preferred for marine or harsh corrosion. Hot-dip galvanized pairs with galvanized fasteners for outdoor structural work.
Use a lock washer when vibration or movement could loosen the joint; choose a flat washer for surface protection and load distribution.
Use one on soft materials, enlarged holes, or when you want better load distribution and surface protection.
Use a bonded-seal style when you want a metal backing with an elastomer to help keep liquids or dust out.
Construction, machinery, vehicles, electrical panels, plumbing fixtures, and general maintenance and repair.