Custom Washers — Flat, Spring & Special Washers

What this part is and where it is used

A custom washer is defined by three numbers — inside diameter, outside diameter and thickness — and they are not independent. On an M10 bolt the shank is 10 mm, a normal clearance hole is 10.5 mm and a plain washer bore is 10.5 mm; change any one of those and the other two have to move. That is why a washer that has to fit a specific joint is a machined part rather than a catalogue item. Custom washers are thin, generally unthreaded discs placed under a nut or bolt head to spread load, protect the part surface and, in the case of lock washers, resist loosening.

Buyers order custom washers when a standard flat washer does not fit: a specific ID/OD ratio, an unusual thickness, a spring form, or a material such as brass, titanium or 316L. They are usually specified as fasteners and washers sets alongside matching parts from our custom nuts and custom bolts pages.

Washer types we machine

The types of washers most orders fall into:

• Flat washers — plain discs for load spreading and surface protection.
• Spring washers — split rings that hold tension and resist loosening.
• Lock washers — internal- or external-tooth forms that bite into the joint face.
• Fender washers — large outside diameters for oversized holes and thin material.
• Square washers — a square plate with a larger bearing area, common under square-head bolts and in plate work.
• Custom profile washers — non-round OD shapes, tabs, slots and keyways cut to print.

A square washer, a toothed lock washer or a profile with a locating tab follows the same route for us — the blank is turned or milled from bar or plate, then the profile is cut to your drawing. Matching custom nuts and custom bolts come from the same shop.

Thickness, diameter and flatness

Inside diameter, outside diameter and thickness all follow your drawing — we do not fit your washer into a stock size table. Shim and spacer thickness is held to ±0.01 mm on precision features, and general dimensions to ISO 2768-m unless the print states otherwise. Faces are cut parallel, so a shim stack stays even part to part and the washer seats flat against the joint.

Thickness matters most where the washer also acts as a spacer, while flatness matters where the washer face carries clamp load. Tell us which faces are functional and we machine them accordingly — see our tolerances and drawing requirements pages.

Materials, threads and finishes

Common materials are aluminium 2024, 5052, 6061 and 7075; stainless steel 301, 303, 304, 316, 316L and 17-4PH; carbon and alloy steel 1045, 1215, 4140, D2 and O1; brass, copper and bronze; and titanium. Metal washers for corrosion use stainless steel — 316L where chlorides are present, 301 where the washer has to take a spring temper — while brass, bronze and copper suit conductivity and instrument work; the grade list is on our materials index, with detail on the stainless steel parts, aluminium parts, steel parts, brass and copper parts and titanium parts pages.

Most washers are unthreaded, but a threaded washer follows metric or inch references per your print — see our thread standards guide. Finishing runs through our vetted partner network under one quality process: zinc plating, black oxide, passivation and anodizing for aluminium. Inside diameter, outside diameter and thickness are all held to the print, so a shim stack stays consistent from part to part.

Sizing a washer: the three numbers that must agree

A washer is defined by three dimensions, and they are not independent — change one and the other two have to move.

The inside diameter has to clear the shank or thread it passes over and still be smaller than the clearance hole, so the washer bears on the joint face instead of falling through. For an M10 bolt the shank is 10 mm, a normal clearance hole is 10.5 mm to 11 mm, and a standard plain washer is 10.5 mm ID — which puts the bore just at the clearance hole and the bearing face 4 mm out from the hole edge.

The outside diameter sets the bearing area. Make it too small and the washer embeds into the joint face or dishes under preload; make it too large on a thin section and the washer itself bends, lifting the contact away from the hole edge where the load actually is. A useful working range for a general flat washer is an outside diameter of about twice the bolt diameter.

The thickness decides whether the washer is only spreading load or also spacing. Once a washer is doing a spacer job its thickness becomes a precision feature rather than a nominal one, and that is where a shim stack machined to ±0.01 mm earns its cost against a stamped part bought by nominal thickness.

Preload: why washer thickness is an engineering number

A bolted joint holds because the bolt is stretched and the joint is compressed. The washer sits in that load path, and everything it does — spreading load, protecting the surface, resisting embedding — changes how much of the tightening torque becomes clamp load.

A soft or thin washer embeds into a rough surface under the bolt head and loses preload within hours of assembly. A hardened washer resists embedding, keeps more of the torque as tension, and holds the joint tight. On a joint that sees vibration or thermal cycling, that difference decides whether the fastener stays tight.

This is also why a washer that looks interchangeable is not. Going from a 1.6 mm to a 1.0 mm washer changes the grip length and the joint stiffness, and on a short bolt the preload change can be large enough to matter. If the washer thickness is functional, say so on the drawing rather than leaving it to the nearest stock thickness.

The washers that are not flat

Four washer families do work that a flat disc cannot, and they are not interchangeable with one another.

Split lock washers bite into the bolt head and the joint face as they flatten. They add a small amount of spring travel and resist loosening on joints that see mild vibration, and their holding power is limited — on a joint that must not move at all, a toothed or a chemical locking method does the job better.

Toothed lock washers have internal or external teeth that bite into the contact surfaces. They resist rotation well and they mark the surface they bite, which matters on a plated or cosmetic face.

Belleville, or disc spring, washers are conical and give a controlled load-deflection curve. Stacked in series they add travel at low load, stacked in parallel they add load at low travel. They are used where a joint has to hold preload through thermal expansion, and where a spring rate has to be designed rather than assumed.

Spring washers in the wave or curved form take up small amounts of play in assemblies where a light, consistent load is wanted — instrument panels, electrical contacts and similar places where the load is a positioning force rather than a clamp load.

Material selection, and the pair it touches

The washer is usually the part that touches two different materials, which makes it the place galvanic corrosion starts.

Matching stainless washers to stainless fasteners on aluminium structure is the standard trap. In a dry indoor assembly the pair is fine; where condensation or wash-down is present, the aluminium becomes the anode and corrodes around the washer. The fixes are a coated or plated washer, an insulating washer, or a change of material — and the drawing has to say which.

Material grade follows the service. Grade 304 is the general stainless choice, 316 or 316L where chlorides are present, and 301 where the washer has to hold a spring temper as a spring or lock form. Carbon and alloy steel covers 1045, 1215 and 4140 with plating for corrosion resistance, and D2 or O1 where the washer doubles as a wear surface. Brass, bronze and copper are chosen for conductivity and instrument work rather than for strength, and titanium for weight-critical joints.

Plated washers have one more consideration: the plating on a washer takes more abrasion than the plating on a bolt head, because the washer is what slides as the fastener is tightened. A washer intended to turn under load is better made from stainless than from plated steel.

Flatness, burrs and the faces that carry load

A flat washer is a bearing surface, so the flatness of its faces is a functional dimension rather than a cosmetic one.

Two things spoil it. Stamping leaves a burr on one side and a rounded edge on the other, and the burr sits exactly where the load should transfer. And thin parts distort as they are cut, so a washer that measures correct at the outside diameter can still rock on a surface plate.

Machining from bar or plate removes both problems. The faces are turned or milled parallel, the edges are clean, and the washer seats against the joint over its full face. That is why a machined washer costs more than a stamped one and why it is the right part when the washer also sets alignment, carries clamp load on a sealed face, or forms part of a shim stack.

Where flatness matters, name it on the drawing as a total indicated runout or a parallelism figure against thickness, rather than leaving it as an implied condition.

Hardness and what it changes

Hardness decides whether a washer spreads load or becomes part of the problem.

A washer softer than the surface it bears on will deform first. Under a high-strength fastener, a soft washer dishes and the effective bearing area shrinks to a ring near the hole — the opposite of what the washer was added to achieve. A washer harder than the joint face can mark it, which matters on a machined or coated surface that has to stay presentable.

The practical rule is to match the washer to the joint. A hardened washer under a high-strength fastener on structural steel, a soft or plastic washer where the job is protecting a painted or delicate surface, and a stainless washer where the job is corrosion resistance and the load is moderate.

Where hardness is specified, give it as a range and name the scale. A single hardness value on a washer drawing usually comes back as a question, because the heat treatment needed to hold it is not free and the range is what the shop actually works to.

Washer drawing mistakes we see

The same handful of errors comes back on quotations.

The most common is a washer that cannot fit its own joint: an inside diameter larger than the clearance hole, so nothing bears on the joint face, or an outside diameter so small that the bearing stress exceeds what the material can take.

Second is a missing thickness tolerance on a washer that is spacing something. Without it, the stack height is whatever the stock thickness happens to be.

Third is a material that is not named, only a finish. “Zinc plated” says nothing about whether the base is 1045 or 1215, and the two machine differently and price differently.

Fourth is hard-to-make geometry specified without a reason — a full-radius edge, an unusual chamfer or a tight concentricity call-out that does not affect function. Each one adds cost, and each one is worth a sentence saying why it is there.

How custom washers are priced

Washer pricing is dominated by three things, and material is the largest.

Material is a big share of the cost on a small part, because a washer has a high surface-to-volume ratio and the material removed to make it is thrown away. Titanium and 316L washers cost several times their steel equivalents before any machining happens.

Machining time is second. A plain flat washer from bar is a fast part; a washer with a non-round profile, a tab, a slot or a keyway is a milled part and the time steps up. A washer with a tolerance on flatness or parallelism adds inspection, not just cutting.

Quantity sets how the cost is amortised. Orders start from 50 pieces; samples take 5–10 days and production 25–35 days, with monthly capacity over 100,000 parts. Send the drawing and we return DFM feedback with a quote within 24 hours — including, where it helps, a note that the washer would be cheaper as a different material or a simpler edge without losing function.

Industries and applications

Flat washers and lock washers appear in automotive, aerospace, medical, oil and gas and electronics hardware assemblies. Shim washers serve precision instruments and machine fixtures where alignment is set to the print.

Why order this part from our factory

We machine custom washers in our own factory in Qidong City, Jiangsu Province. General work is held to ISO 2768-m unless stated on the drawing, with precision features to ±0.01 mm. Orders start from 50 pieces; samples take 5–10 days and production 25–35 days. Monthly capacity runs over 100,000 parts, scheduled flexibly per order. Send a drawing and we return DFM feedback with a quote within 24 hours, then ship with a material certificate (MTR) and pre-shipment photos. WhatsApp us or use the quote form.