M18 x 56 x 4.6mm Form G Flat Construction Washer, Metric, HV140 Mild Steel, BZP, BS 4320

M18 Form G Flat Washer

Form G flat washer designed for secure, reliable fastening in a wide range of applications. Designed with a 20.52mm internal diameter to fit M18 threaded fasteners.

A large heavy-duty washer with an outer diameter that’s up to 3 times the internal diameter which sees them used across many applications. The large external diameter ensures optimal load distribution, enhances joint performance, and protects surfaces from damage. 

A versatile washer used by professionals and DIY enthusiast for numerous applications. These include construction, building projects, engineering assemblies, automotive, DIY and home improvement.

M18 Form G Flat Washer Specifications

• Size (TD): to fit M18 - 18mm
• Diameter (D): 56mm max
• Inner diameter (ID): 20.52mm max
• Thickness (T): 4.60mm max
• Material: HV140 Mild Steel
• Finish: Bright Zinc Plated
  

Part of a larger range of washers available from Fusion Fixings.

FAQs for Form G Flat Washers

What do washers actually do?

Washers are used to spread the load of a bolt or screw, preventing damage to the surface and helping keep the fixing secure. They also reduce loosening and can act as a protective buffer between materials.

Do I really need a washer, or can I skip it?

It depends on the application. In many cases (especially timber, soft materials, or oversized holes), a washer is essential to prevent pull-through and distribute load. In light-duty metal-to-metal fixings, they may sometimes be optional—but still recommended for long-term performance.

Why are some washers so big (like Form G)?

Form G washers have a much larger outer diameter (typically 3× the hole size). This makes them ideal for numerous applications including timber-to-timber fixings, soft materials like plastic and oversized or worn holes.

They spread load over a wider area and prevent fixings from sinking into the material.

What size washer should I use with my bolt?

You should match the internal diameter (ID) of the washer to the bolt size (e.g. M10 bolt = M10 washer). With Form G washers, the outer diameter is much larger than standard, but the hole size still corresponds to the bolt size.

What’s the difference between standard washers and Form G washers?

The key differences are Form G washers are larger and thicker and designed for heavy-duty or load-spreading applications, making them better for timber, construction, and repair work. Standard washers are smaller and used for general-purpose fastening. 

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