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Form C Washers – Zinc (BS 4320)
Wide diameter zinc plated Form C washers designed to increase clamping area and improve load distribution.
Timco Zinc Form C Washers – M12 – Box of 2,000
In stock
£53.33 ex VAT(£63.99 inc VAT)
SKU:
WC12ZBULK
Timco Zinc Form C Washers – M10 – Box of 3,000
Out of stock
£48.33 ex VAT(£57.99 inc VAT)
SKU:
WC10ZBULK
Form C washers are flat washers with a larger outer diameter than both Form A and Form B washers. The increased surface area allows them to distribute load across a wider section of the material, helping reduce surface damage and improving clamping performance.
Manufactured from steel and finished with a clear passivated zinc plating (CR3), these washers are suitable for general internal construction, engineering and assembly work.
Form C washers conform to BS 4320 and are commonly used where additional surface coverage is required under a bolt head or nut.
Specifications
| Material | Steel |
|---|---|
| Finish | Zinc Plated (CR3) – Clear Passivated |
| Standard | BS 4320 |
| Corrosion Rating (1–5) | 1 – Clean, dry & low humidity environments |
| Profile | Form C – Extra wide outer diameter |
Available Sizes
Our zinc Form C washers are available in the following metric sizes.
| Washer Size | To Suit Bolt |
|---|---|
| M6 | M6 bolt |
| M8 | M8 bolt |
| M10 | M10 bolt |
| M12 | M12 bolt |
| M16 | M16 bolt |
| M20 | M20 bolt |
Form C washer dimensions
Because Form C washers have a larger outside diameter than other washer types, they provide increased surface coverage when tightening bolts or nuts.
Typical metric Form C washer dimensions are shown below.
Form C washer dimensions
Form C washers have a wider outer diameter than Form A and Form B washers. As a result, they increase the clamping area and spread load over a larger surface.
The table below shows the listed dimensions for each size in the zinc Form C range.
| Washer Size | Hole Dia. | Outer Dia. (mm) | Thickness (mm) |
|---|---|---|---|
| M6 | M6 | 14 | 1.6 |
| M8 | M8 | 21 | 1.6 |
| M10 | M10 | 24 | 2.0 |
| M12 | M12 | 28 | 2.5 |
| M16 | M16 | 34 | 3.0 |
| M20 | M20 | 39 | 4.0 |
Match the washer size to the bolt diameter. For example, use an M10 Form C washer with an M10 bolt.
Why choose Form C washers?
Form C washers are selected when a larger contact area is required under the fastener.
Because they have the widest outer diameter of the common washer types, they are often used when fixing into softer materials or when the hole size is larger than the bolt diameter.
They can also help prevent the bolt head or nut from pulling into the surface when tightening fixings.
Form A vs Form B vs Form C washers
| Washer Type | Outer Diameter | Typical Use |
|---|---|---|
| Form A | Standard | General construction and fastening |
| Form B | Larger than Form A | Improved load spreading |
| Form C | Largest outer diameter | Maximum surface coverage and clamping area |
Frequently asked questions
What are Form C washers used for?
Form C washers are used when a wider load distribution is required under a bolt head or nut. Their larger diameter helps protect softer materials and improves clamping performance.
When should I use Form C instead of Form A or Form B?
Form C washers are chosen when the surface area around the fixing needs additional support or when the hole size is larger than normal.
Are zinc Form C washers suitable for outdoor use?
Zinc plated washers are generally intended for clean, dry internal environments. For outdoor applications, stainless steel washers are typically recommended.
For applications requiring very wide load spreading, penny repair washers may be a suitable alternative.
Looking for other washer types? Explore our full washer range, including Form A, Form B, Form C, penny repair washers, spring washers and square plate washers.
