Stainless Steel Fender Washers
Oversized outer diameter to spread clamp load over soft, slotted or oversized holes. Produced in 304 and 316/316L stainless to DIN 9021 (ISO 7093 equivalent), plus custom outer diameters made to your drawing.
A wider footprint where the hole can't take a standard washer.
A fender washer is a flat washer with a deliberately oversized outer diameter — roughly three times the bolt nominal — and a relatively thin section. That extra bearing area is what makes it the part of choice when the hole is too large, slotted, soft or out-of-round for an ordinary flat washer to do its job.
By distributing clamp force over a much wider area, a fender washer protects sheet metal, composites, timber and plastics from being pulled through or deformed under the bolt head. We hold the dimensions to DIN 9021 (ISO 7093) and can step outside the standard for special outer diameters, inside diameters and thicknesses.
- Outer diameter ≈ 3× the bolt nominal — far larger than a DIN 125 flat washer
- Spreads load to prevent pull-through on thin or soft materials
- 304, 316 and 316L stainless; bright / passivated as standard
- Standard M4–M20; custom OD, ID and thickness stamped to drawing
What makes a fender washer.
It is defined by proportion, not just size: a large outer diameter relative to the bore, in a thin flat section. That combination is what spreads the load.
Large outer diameter
The defining feature: an OD of roughly three times the bolt nominal — for example a ~24 mm OD on an M8. That wide rim is what bridges an oversized or slotted hole.
Thin, flat section
Relatively thin for its diameter — typically 1.0–4.0 mm across the M4–M20 range. Enough to bear load and protect the surface without adding bulk to the stack-up.
Load spread over area
The wide bearing surface distributes clamp force, preventing the bolt head or nut from pulling through soft sheet, composite, timber or plastic.
DIN 9021 large-OD fender washer dimensions.
Metric dimensions in millimetres, per DIN 9021 (ISO 7093 equivalent). The outer diameter is approximately three times the thread nominal. Tolerances per the standard; mill test certificates (MTC / EN 10204 3.1) available on request.
| Thread d | Inside dia d1 | Outside dia d2 | Thickness s |
|---|---|---|---|
| M4 | 4.3 | 12 | 1.0 |
| M5 | 5.3 | 15 | 1.2 |
| M6 | 6.4 | 18 | 1.6 |
| M8 | 8.4 | 24 | 2.0 |
| M10 | 10.5 | 30 | 2.5 |
| M12 | 13 | 37 | 3.0 |
| M14 | 15 | 44 | 3.0 |
| M16 | 17 | 50 | 3.0 |
| M20 | 22 | 60 | 4.0 |
We regularly stamp non-standard outer diameters, inside diameters and thicknesses to drawing. Send your specification and we will confirm feasibility and pricing — typically within ~1 business day.
Where fender washers earn their keep.
Anywhere the hole is larger, softer or more slotted than a standard flat washer can handle — and the joint still has to hold.
Sheet Metal
Bridges oversized or slotted holes in thin gauge, spreading load to prevent pull-through.
Automotive Body
The original "fender" use — securing body panels and brackets over enlarged or rusted holes.
Marine
Corrosion-resistant 316 fender washers for hull fittings, decking and exposed hardware.
Signage
Mounting panels, channel letters and fascia where wide bearing protects soft or thin substrates.
Solar PV
Module mounting and clamping where outdoor exposure demands a corrosion-grade, load-spreading washer.
General Assembly
Plastics, composites and timber fastening that needs a large, smooth bearing face.
Grade and finish, matched to the environment.
Fender washers spend their life on the surface of a joint, often outdoors — so material and finish matter as much as dimensions.
304 — general duty
Strong general corrosion resistance for indoor, structural, automotive-body and most architectural fastening. The cost-effective default for sheet metal and signage.
- Sheet metal · automotive body · signage · general assembly
316 — marine & coastal
Added molybdenum for chloride and salt-spray resistance. The grade to specify for marine hardware, coastal solar and any wash-down or weather-exposed mounting.
- Marine · coastal solar · chemical · exposed outdoor
Standard finish
Bright / passivated as supplied, for clean appearance and a stable, corrosion-resistant surface out of the box.
On request
Polished, electropolished, black, zinc or Geomet finishes to match appearance, environment or assembly spec.
Documentation
Mill test certificates (MTC / EN 10204 3.1) and PMI available on request for export and compliance.
Fender washer questions, answered.
What is the difference between a fender washer and a flat washer?
A fender washer has a much larger outer diameter for its bore — typically about three times the bolt nominal — while a standard flat washer (DIN 125) has an OD only slightly larger than the hole. The oversized OD lets a fender washer bridge soft, slotted or oversized holes and spread clamp load over a far wider bearing area. Fender washers are also relatively thin for their diameter.
What sizes and outer-diameter options are available?
We produce DIN 9021 / ISO 7093 fender washers from M4 to M20 as standard, with outer diameters from 12 mm up to 60 mm and thicknesses from 1.0 mm to 4.0 mm. The outer diameter is roughly three times the bolt nominal. Larger or non-standard outer diameters are available on request — the dimension table above shows representative sizes, with the full range per the standard available on request.
Can you make custom outer diameters?
Yes. Custom and non-standard fender washers are a core part of our work. We stamp special outer diameters, inside diameters and thicknesses to your drawing or sample in 304, 316 or 316L stainless, with first-article inspection and material certificates available on request. Send a print or sample and we will confirm feasibility and pricing, typically within ~1 business day.
Tell us what you need.
Send specs or a drawing and we will come back with pricing, lead time and material options. No account, no minimum to ask.
- ✓ 304 / 316 / 316L, DIN & ASME or custom
- ✓ Replies from engineers, typically within one business day
- ✓ Samples and material certificates available