Washers · Trade series (vulcanised fibre washer)

A2 (304) Stainless Steel Insulating Fibre Washers

Mechanical properties, corrosion behaviour and the full dimensional range for this grade.

A2 Stainless Steel Insulating Fibre Washers are supplied to ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70. Corrosion behaviour is good general corrosion resistance, the material is largely non-magnetic, and the usable service range is approx. -200 °C to +400 °C, subject to the property class and the joint. In practice this grade is the most common stainless group for indoor and general outdoor fasteners.

Grade: ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70
Corrosion resistance: Good general corrosion resistance
Magnetic response: Largely non-magnetic
Service temperature: approx. -200 °C to +400 °C, subject to the property class and the joint

Property values are typical for the grade. Certified mechanical test data is available on request for production orders.

A2 Stainless Steel Insulating Fibre Washers are supplied to Trade series (vulcanised fibre washer). The grade provides good general corrosion resistance and is largely non-magnetic; the practical service range is approx. -200 °C to +400 °C, subject to the property class and the joint. Property data, grade comparison and the full size table follow.

Why Choose A2 Stainless Steel for Insulating Fibre Washers

The most common stainless group for indoor and general outdoor fasteners. For insulating fibre washers, this matters when good general corrosion resistance is the primary requirement.

Mechanical & Physical Properties

Grade designation	ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70
Magnetic response	Largely non-magnetic
Service temperature	approx. -200 °C to +400 °C, subject to the property class and the joint
Corrosion characteristic	Good general corrosion resistance

Corrosion Behavior in Service

A2 (304) gives excellent atmospheric and most-water corrosion resistance and is the most common stainless for Insulating Fibre Washers in indoor and general outdoor service. In chloride-bearing environments (marine air, road salt, swimming pools) consider stepping up to A4 (316).

Galvanic & Galling Considerations

For stainless insulating fibre washers the compatibility question is galvanic rather than galling: joined to aluminum or galvanized steel in wet service, stainless drives corrosion of the less-noble metal. Isolate with a coating, sleeve or non-conductive washer where the joint sees moisture. Note also that stainless is softer than hardened carbon steel, so where the part carries a wear or shear duty, check the load against the grade before substituting.

Using Stainless Fasteners in Aluminum

The galvanic couple here runs the wrong way: aluminum is the less noble metal, so it corrodes and the fastener does not. What governs the rate is the ratio of areas — a large anode and a small cathode is a tolerable combination, the reverse concentrates the attack into thin material around the hole. An isolating washer plus sealant breaks the circuit; where that is impractical, match the fastener to the substrate.

Sizes of Insulating Fibre Washers Available in A2 Stainless Steel

For bolt size	Inner diameter d1 (mm)	Outer diameter d2 (mm)	Thickness t (mm)	Dielectric strength (kV/mm)	Max temperature (u00b0C)	Material	Moisture
M3	3.2	7.0	0.5	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M4	4.3	9.0	0.5	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M5	5.3	10.0	0.8	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M6	6.4	12.0	0.8	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M8	8.4	16.0	1.0	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M10	10.5	20.0	1.0	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use

Technical Drawing

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Specification

Item / category Standard Size(s) Material / finish Quantity

Business Information

Company * Contact Name * Email * Phone (with country code) Country / Region

Notes

Dimensions & Specifications (Trade series (vulcanised fibre washer))

For bolt size	Inner diameter d1 (mm)	Outer diameter d2 (mm)	Thickness t (mm)	Dielectric strength (kV/mm)	Max temperature (u00b0C)	Material	Moisture
M3	3.2	7.0	0.5	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M4	4.3	9.0	0.5	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M5	5.3	10.0	0.8	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M6	6.4	12.0	0.8	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M8	8.4	16.0	1.0	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use
M10	10.5	20.0	1.0	10	105	Vulcanised fibre	Hygroscopic u2014 indoor use

Applications & Industries

The sectors that buy Insulating Fibre Washers, and the duty each one buys them for. Stocked from M3 to M10 (nominal bolt size).

Industries that specify Insulating Fibre Washers

Food & pharma equipment Non-marking, non-contaminating washers in washdown areas.
Electrical & electronics Insulating and isolating fixings in panels and boards.
Chemical & process Chemically resistant seating under a fastener.
Machine building & OEM Setting bearing area on soft alloy, plastic and oversized holes.
Timber & construction Large-diameter washers that stop pull-through in softer material.
Rotating & vibrating plant Spring, tooth and wedge types that maintain or lock bolt tension.

Typical applications

protecting a soft or finished surface under a head
insulating a fastener electrically from the panel
separating dissimilar metals to break a galvanic cell
maintaining bolt tension in a joint that settles
spreading clamp load over a soft or oversized bearing face
protecting a painted or plated surface under a turned nut

Service conditions to specify against

Marine and coastal: Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
Hardness matters: Under a high-strength bolt a soft washer embeds into the joint and preload is lost — specify a hardened washer for structural bolting.

Full application guide: where Insulating Fibre Washers are used, how to specify them, and the cases they are wrong for

Inside the plant

Manufactured in our own plant

This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided.

01

Cold heading

Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail.

Head dimensions and under-head radius checked at set-up and per shift.
02

Thread rolling

Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch.

Go / no-go ring gauges to ISO 965 tolerance class 6g.
03

Heat treatment

Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it.

Core hardness and tensile tested per lot to ISO 898-1.
04

Surface treatment

Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list.

Coating thickness and neutral salt spray hours to ISO 9227.

Frequently Asked Questions

Can A2 Stainless Steel replace plated alloy steel structurally?

Only at the standard strength classes — A2-70 / A4-80 are roughly equivalent to class 7 steel; A4-100 reaches class 8.8. For class 10.9 or 12.9 strength, plated alloy steel is required.

Are A2 Stainless Steel Insulating Fibre Washers magnetic?

A2 Stainless Steel Insulating Fibre Washers are largely non-magnetic.

What corrosion resistance do A2 Stainless Steel Insulating Fibre Washers offer?

A2 Stainless Steel Insulating Fibre Washers provide good general corrosion resistance with a service range of approx. -200 °C to +400 °C, subject to the property class and the joint.

Should I choose A2 Stainless Steel or A4 (316) for Insulating Fibre Washers?

For Insulating Fibre Washers, A2 Stainless Steel suits general indoor and outdoor use; A4 (316) is preferred for marine, coastal and chemical environments. Choose by corrosion exposure first.

How do I request a quotation?

Use the technical drawing on this page to pick the exact configuration, then submit it with the quote form. We respond within one business day.