Flat & Round Washers

AIMS Industrial stocks over 130 flat and round washers across metric and imperial sizing, covering mild steel (plain, zinc plated, hot-dip galvanised and passivated finishes), 304 and 316 stainless steel, brass, copper, aluminium, nylon and fibre — from Champion, Hobson, Bremick, Inox World and GJ Works. A flat washer is the plainest, most-used fastener component in any workshop: a flat ring that sits under a bolt head or nut, spreading clamping load over a wider bearing area, protecting the joint face from indentation, and giving the nut a smooth, flat surface to turn against as it's tightened. This range covers the everyday flat/round washer job — load distribution and surface protection under a standard bolted joint. If you're after a vibration-resistant washer (Nord-Lock wedge-lock, Schnorr conical spring, or a split spring washer), a fluid-sealing washer (Dowty/bonded seal, copper crush washer) or a vibration-isolator cushioning washer, see our full washers range and our dedicated Sealing & Cushioning Washers collection — this page sticks to plain flat and round bearing washers. For more on selection, see our Types of Washers: Flat, Spring, Lock, Structural & Sealing Explained.

Quick Reference — Flat & Round Washer Range

Form A is the workshop default and the right choice unless you have a specific reason to go wider or harder. Step up to Form B (Large/Supa) when the substrate is soft, compressible or the clearance hole is oversized; step up to a hardened Sampson or Engineers washer under high-tensile bolt heads where a standard washer would deform under torque. If you're not sure which one your job needs, give our team a call — it's a two-minute conversation and it saves a return trip to the shed.

Form A vs Form B vs Hardened Washers

Form A (Standard / Narrow) — the default

A Form A flat round washer has an outside diameter roughly twice the bolt diameter — enough bearing area for the great majority of general fastening work without wasting material or crowding a tight bolt pattern. In Australia this is the washer specified to AS 1237 (the Australian Standard for plain washers), corresponding closely to the international DIN 125A reference most trade catalogues still quote alongside it. Hobson, Bremick and Inox World all supply Form A washers across the common metric range, in mild steel, 304 and 316 stainless.

Form B (Large / Supa / Wide)

Form B — sold in our range as the "Large" or "Supa" flat round washer — has a noticeably bigger outside diameter for the same bolt size, spreading clamping load over a wider bearing area. Reach for a Form B washer when the material underneath is soft or compressible (timber, plasterboard, thin sheet, composite decking), when the clearance hole is oversized or slotted, or when a Form A washer would let the bolt head or nut sink into the surface under load. Hobson's Large/Supa Flat Round Washer is stocked in plain, zinc plated and hot-dip galvanised finishes.

Hardened Washers — Sampson, Engineers & High-Tensile

Hobson's Sampson and Engineers washer ranges, and Champion's high-tensile flat washers, are case-hardened to roughly 35–45 HRC rather than mild steel. A standard flat washer will compress and deform under the higher preload of a Grade 8.8 or 10.9 bolted joint, effectively relaxing the clamp load — a hardened washer holds its shape and keeps the joint tight. They're specified under high-tensile bolt and nut heads, wherever a spring or lock washer needs a hard, flat bearing surface to seat against, and generally anywhere the fastener grade steps up above a standard commercial bolt. If your job calls for a fully certified structural bolting assembly (HSFG bolting to AS/NZS 1252), talk to our team — those assemblies are specified as matched bolt/nut/washer sets and we'll confirm the right combination rather than guess at it here.

Metric vs Imperial Sizing

Metric flat round washers are specified by the bolt size they fit — an M8 washer suits an M8 bolt — and our metric range runs from M2 up to M48 across the Inox World stainless line, with mild steel and Hobson/Bremick ranges commonly stocked from M3 to M30. Imperial washers are specified differently: by inside diameter × outside diameter × gauge (thickness), because a single imperial bolt size is often available with more than one washer OD — for example a 1/4" bolt might take a 1/4" x 5/8" x 18G standard washer or a 1/4" x 1 1/4" x 16G large washer, depending on the job. Our imperial range runs from 1/8" through to 1" and above, in both the standard and large/wide OD options, so check the full ID × OD × gauge callout rather than the bolt size alone when ordering imperial.

If you're working from an existing drawing or replacing washers on an imported machine, don't assume metric and imperial washers are interchangeable even where the ID is close — a 1/4" (6.35mm) bolt and an M6 (6mm) bolt look similar but the washer ID, and often the OD and thickness, won't match cleanly. When in doubt, measure the existing washer or bolt and we'll match it for you.

Material & Finish Guide

Mild Steel — Plain, Zinc Plated, Passivated & Hot-Dip Galvanised

Mild steel is the most economical and most-stocked flat washer material, and the finish is what determines where it can be used. Plain (uncoated) mild steel is for dry, indoor, short-term or immediately-painted applications only — it will surface-rust quickly in any damp or outdoor environment. Zinc plating (including zinc yellow and zinc black passivate finishes) gives a thin sacrificial coating suited to general indoor and short-exposure outdoor use. Hot-dip galvanising builds a much thicker, more durable zinc coating and is the right call for washers that will sit outdoors, in a construction application, or anywhere long-term corrosion resistance matters more than a tidy finish.

304 & 316 Stainless Steel

304 (A2) stainless is the standard grade for general corrosion resistance, food-grade equipment and most indoor-to-sheltered-outdoor applications. 316 (A4) stainless adds molybdenum for genuine chloride resistance — specify it for marine hardware, coastal structures, food and chemical processing, and anywhere washdown or salt exposure would pit a 304 washer over time. Match the washer grade to the bolt and nut grade in the same joint; mixing carbon steel with stainless in a wet or corrosive environment sets up galvanic corrosion, with the less noble metal — usually the plain steel — corroding preferentially.

Brass, Copper & Aluminium

Brass flat round washers (stocked to AS 1237 sizing) suit electrical earthing points, decorative brass-fitting work and non-sparking applications around flammable atmospheres. Copper and aluminium washers are soft, single-use crush-seal materials — Champion's copper and aluminium washer ranges and assortment kits (including sump plug and fuel injection copper washer kits) are sized for banjo bolts, drain plugs and fuel system fittings, where the washer needs to deform slightly under torque to seal against surface irregularities rather than stay rigid like a structural flat washer.

Nylon & Fibre

Nylon 66 flat round washers provide electrical insulation and prevent galvanic contact between dissimilar metals or coated surfaces — useful anywhere a metal washer would short a circuit or set up corrosion between an aluminium panel and a steel bolt. Fibre washers are a firm, compressible gasket-style washer for general-purpose light sealing rather than structural load distribution. Neither should be substituted for a steel or stainless washer in a load-bearing structural joint.

Assortment Kits vs Loose Stock

A large share of this range is Champion assortment and refill kits — copper, aluminium, fibre, spacing steel, high-tensile and flat steel washer kits running from around 100 pieces up to 600+ pieces, boxed by size so a service van or maintenance store always has the right washer on hand without ordering single sizes ad hoc. If you're setting up a new van, ute or store cage, a kit is the fastest way to get broad size coverage in one purchase; if you're running a specific job or production line, loose stock in a single size and material is usually the more economical option per piece. We can supply both, and can also put together a custom bulk pack to your own size and material spread for an ongoing maintenance contract — request a quote and tell us what you need to cover.

Brands We Stock

Hobson supplies our broadest flat/round washer range — standard, large/supa, Sampson and Engineers hardened washers, plus brass and nylon options, in plain, zinc, galvanised and passivate finishes. Bremick covers the core metric and imperial mild steel range in plain, zinc and hot-dip galvanised finishes. Inox World is our dedicated stainless steel line, with 304 and 316 flat round washers across the full metric M2–M48 and imperial 1/8"–1"+ range. Champion supplies the copper, aluminium, fibre, spacing and high-tensile washer ranges, largely as assortment and refill kits, along with GJ Works' own fastener assortment kits. A small number of Bumax stainless high-tensile washers and Nord-Lock wedge-lock washers also carry the Flat Round Washers tag in our system because they're supplied and specified alongside standard flat washers — but they're a different locking technology to a plain flat washer; see Nord-Lock or the full washers range if vibration-resistant locking, rather than simple load distribution, is what you're after.

Order Flat & Round Washers from AIMS

Not sure which form, material or size your job needs — or ordering in bulk for a fabrication run, maintenance contract or construction project? Our team can confirm stock, match an existing washer from a sample or drawing, and put together competitive bulk or trade pricing. Call us on (02) 9773 0122, get in touch through our contact page, or request a quote for a project or ongoing supply.

People Also Ask

What is a flat washer used for?

A flat washer sits under a bolt head or nut to spread clamping load over a wider area, stopping the fastener from denting, pulling through or embedding into the joined material. It also protects a finished surface from tool marks during tightening and gives the nut a smooth, flat bearing face to turn against.

What's the difference between a flat washer and a round washer?

In everyday trade language "flat washer" and "round washer" describe the same plain, flat-ring washer — the terms are used interchangeably, which is why we list this range as Flat & Round Washers. Neither term refers to a spring, lock or wedge-lock washer, which are different products entirely.

What size flat washer do I need for an M10 bolt?

A standard Form A metric flat washer for an M10 bolt has an inside diameter just over 10mm to clear the bolt shank, with an outside diameter roughly twice that. Our metric flat washer range covers M10 in mild steel, 304 and 316 stainless — check the individual product page for exact ID/OD/thickness for the specific finish and brand you need, since Form A and Form B options differ in OD for the same bolt size.

Do I need a flat washer under every bolt?

As standard practice, yes — a flat washer protects both the surface and the bolt head or nut from damage, and gives a consistent, flat bearing surface for accurate torque. On structural, safety-critical or high-vibration joints a washer is effectively mandatory. It's occasionally omitted by design on low-load fastening into hard, flat steel where surface damage isn't a concern — when in doubt, use the washer.

Should I use a stainless or a mild steel flat washer?

Use mild steel (zinc plated or hot-dip galvanised, depending on exposure) for general indoor and standard outdoor fastening where cost matters and the environment isn't aggressive. Use 304 stainless for food-grade, general corrosive or indoor/sheltered-outdoor work, and step up to 316 stainless for marine, coastal, chemical or washdown environments where 304 would eventually pit from chloride exposure.

Can I mix a stainless washer with a zinc-plated or galvanised bolt?

It's not recommended in a wet or exposed environment. Mismatched metals in contact with moisture set up galvanic corrosion, with the less noble metal — typically the plated or galvanised steel — corroding preferentially at the point of contact. Match washer material to the bolt and nut material wherever the joint will see moisture, weather or washdown.

What's the difference between a standard and a large (Supa) flat washer?

A standard (Form A) washer has an outside diameter roughly twice the bolt diameter and is the default for general fastening. A large or "Supa" (Form B) washer has a noticeably bigger outside diameter for the same bolt size, spreading load over more area — specified for soft materials, oversized clearance holes, or slotted holes where a standard washer wouldn't bridge the gap.

Why would I need a hardened flat washer instead of a standard one?

A standard mild steel washer can compress and deform under the higher preload of a high-tensile (Grade 8.8/10.9) bolted joint, letting the clamp load relax over time. A hardened washer — such as Hobson's Sampson or Engineers range, hardened to roughly 35–45 HRC — holds its shape under that higher load and keeps the joint properly tensioned.

Can I buy flat washers in bulk for a project?

Yes. Beyond single-size stock, we carry Champion assortment and refill kits from around 100 to 600+ pieces for maintenance and service use, and can supply project-volume quantities in a specific size and material, or put together a custom bulk pack to your own size spread. Request a quote with your quantities and we'll confirm stock and pricing.

What's the difference between a copper washer and a standard steel flat washer?

A copper washer is deliberately soft — it's designed to crush and deform slightly under torque to form a seal against surface irregularities on a fitting such as a sump plug or fuel banjo bolt, and is generally single-use. A standard steel or stainless flat washer is rigid by design — it's meant to hold its shape and distribute load, not deform, and can be reused.