Stainless Steel Big OD Washer

Choosing the Right Big OD Washer

(Large Outside Diameter / Penny / Fender / Repair Washer)

1) What is a Big OD washer & when should you use it?

A Big OD washer is a plain washer with a much larger outside diameter than standard.
It is designed to:

Spread load over a much larger area

Reinforce thin or soft materials (sheet metal, plastics, timber, composites)

Cover oversized, slotted or slightly damaged holes

Prevent pull-through of the nut/bolt head

Use a Big OD washer when:

You are bolting through thin sheet, soft material or insulation panels

The hole is oversized or slotted, and you need more bearing area

You want to repair/cover a damaged hole without reworking the part

You need to reduce local crushing and deformation under the bolt head or nut

Typical applications:

Sheet-metal ducting, cladding, roofing & facades

Electrical/AC brackets, light supports, cable trays

Timber fixing & plywood panels

Automotive & bodywork (fender washers)

Repair/maintenance jobs where a normal washer is too small

2) Big OD vs standard washer – what’s the difference?

Standard plain washer (normal OD):

Used for general bolting with normal plate thickness.

Spreads load but within a limited area.

Big OD washer (large OD / penny / fender washer):

Has a much larger outside diameter for the same bolt size.

Spreads load over a wider area, which:

Reduces bearing pressure,

Protects thin or soft substrates,

Minimises pull-through and local deformation.

Rule of thumb:

Normal plates & sections → standard washer.

Thin sheet / soft material / slotted or oversized holes → Big OD washer.

Mechanical Properties (Guide) – Big OD Washer

Big OD washers are primarily about bearing area and stiffness, not about high tensile strength like bolts. The key properties are material grade, hardness, thickness, and OD relative to the load.

1) Mild steel Big OD washers (standard)

Typical characteristics:

Material: low carbon steel.

Usually non-hardened or lightly cold-worked.

Suitable for light-to-medium duty load spreading applications.

Functional behaviour:

Good for distributing clamping force on:

Thin steel sheet,

Aluminium panels,

Plastics,

Timber & plywood.

Under higher bolt preload, thin MS Big OD washers can:

Dish/bend slightly,

Indent into very soft material beneath.

For highly loaded structural joints, a standard thin Big OD washer may not be enough – consider thicker or hardened options.

2) Hardened / structural Big OD washers

Some Big OD washers are manufactured from higher strength or hardened steel, especially for heavier structural or anchoring applications.

Typical characteristics:

Made from medium carbon or alloy steel, properly heat-treated.

Higher hardness and better resistance to bearing deformation.

Often thicker than standard fender/penny washers.

Functional behaviour:

Can carry higher compressive bearing loads without significant permanent deformation.

Better suited for:

Anchor bolt plates,

Heavy equipment fixings,

High-tension joints where a large bearing area is required.

When used with high-tensile bolts, hardened Big OD washers help prevent embedment and loss of preload.

3) Stainless steel Big OD washers (A2 / A4)

Typical characteristics:

Material: A2 (304) or A4 (316) stainless steel.

Provide medium to high bearing strength plus excellent corrosion resistance.

Functional behaviour:

Ideal for:

Stainless façades & cladding,

Outdoor brackets and signages,

Food & pharma plant structures,

Marine & coastal fixtures.

On very soft substrate (wood, plastic), they still may indent if very high preload is applied; in that case, a thicker Big OD washer or small backing plate may be preferred.