Carbon Steel Flat Washer — Factory Direct Supplier | Huaxia-Steel

A flat washer looks like the simplest part in a bolted joint and is usually the first item a buyer tries to cost down. It is also the component that decides whether a bolted assembly keeps its clamp load after a year outdoors, whether a coated panel is damaged during tightening, and whether a 10.9 bolt bears on a surface large enough to develop its proof load. We supply carbon steel flat washers in DIN 125 A/B, DIN 126, DIN 9021, ISO 7089/7090/7091, ASTM F844 and USS/SAE patterns, from M3 to M64 and 1/4″ to 2″, in thicknesses from 0.5 mm to 12 mm, with zinc plating, hot dip galvanizing, black oxide or plain finish. Hardness, inside diameter and flatness are controlled per lot, and every carton carries a lot number traceable to the steel coil.

Product Overview

A flat washer does three jobs. It spreads the bolt’s clamp load over an area large enough to prevent the clamped material from yielding; it protects the surface finish of the part from the rotating nut or bolt head; and, in a hardened version, it provides a bearing surface hard enough to let a high-strength fastener reach its proof load without embedding into soft steel.

The distinction between an unhardened and a hardened washer is the single most misunderstood point in washer purchasing. An unhardened washer to DIN 125 A has a hardness of about 200 HV, which is adequate under an 8.8 bolt. Put the same washer under a 10.9 bolt tightened to proof load and the washer deforms, the joint loses preload within hours, and the bolt eventually fatigues. The hardened DIN 125 B at 300 HV, or the ASTM F436 structural washer, exists precisely for that case. Selling one for the other is a common substitution and an expensive one.

Specifications

Parameter	Range / value
Size	M3 – M64, 1/4″ – 2″
Outside diameter	7 – 160 mm depending on pattern
Inside diameter	3.2 – 66 mm, tolerance H13 (metric) / +0.5 mm typical
Thickness	0.5 – 12 mm; tolerance ±0.1 mm for thin, ±0.3 mm for heavy
Hardness	140 HV (DIN 125 A light), 200 HV (standard), 300 HV (DIN 125 B / ISO 7090)
Flatness	≤ 0.1 mm for Ø ≤ 30 mm; ≤ 0.2 mm above
Material	Low carbon 1008/1010 (standard), medium carbon 1045 for hardened types
Coating	Zinc plated 3–12 µm, hot dip galvanized 40–80 µm, black oxide, mechanical zinc, plain
Standard	DIN 125 A/B, DIN 126, DIN 9021, ISO 7089/7090/7091/7093, ASTM F844, ASTM F436, USS/SAE
Packing	25 kg cartons, 500–1000 kg pallets, or counted poly bags

Available Grades and Patterns

Pattern selection usually follows the bolt standard, but the dimensions differ enough between systems that a “M12 washer” from a European drawing and an “1/2 inch washer” from an American one are not interchangeable, even though both nominally suit a 12 mm fastener. The table below gives the practical mapping.

Standard	Type	Hardness	Typical pairing
DIN 125 A	Standard metric, normal thickness	200 HV	Class 8.8 bolts, general assembly
DIN 125 B	Hardened metric	300 HV	Class 10.9 bolts, high preload
ISO 7089 / 7090	Metric, 200 HV / 300 HV	200 / 300 HV	ISO-drawn assemblies
DIN 126 / ISO 7091	Larger OD, thinner	200 HV	Soft or slotted materials
DIN 9021 / ISO 7093	Fender washer, very large OD	140–200 HV	Sheet metal, plastics, timber
ASTM F844	General purpose inch washer	Unhardened	Inch bolts up to Grade 5
ASTM F436	Hardened structural washer	38–45 HRC	A325 / A490 structural bolts
USS / SAE	Inch wide / narrow pattern	Unhardened	General inch fastening

For galvanized assemblies, specify washers galvanized to the same coating weight as the nut and bolt — a 40 µm washer under an 80 µm bolt leaves a thin spot in the corrosion protection exactly where water collects. For stainless-to-carbon joints, an isolating washer in nylon or EPDM is worth discussing, because a carbon washer in contact with a stainless plate will corrode first and stain the assembly.

Manufacturing Standards and Process

• DIN 125 / ISO 7089 — the default metric plain washer, defining OD, ID, thickness and chamfer.
• ISO 4759-1 — tolerances for fasteners, product grades A, B and C, which govern how much OD and thickness variation is acceptable.
• ISO 4042 — electroplated coatings, thickness classes and the requirement for hydrogen relief bake on hardened parts.
• ASTM F844 — washers for general use, covering dimensions and hardness for inch sizes.
• ASTM F436 — hardened steel washers for structural joints, requiring 38–45 HRC and a specified circularity.
• ASTM A153 / ISO 10684 — hot dip galvanizing of fasteners and washers, including centrifuge requirements to clear the hole.

Our process is cold stamping from coil, followed by deburring, tumbling to remove sharp edges, and heat treatment only for the hardened grades. Hardened washers are quenched and tempered to 300 HV or 38–45 HRC, then baked after plating to relieve hydrogen. Flatness is checked on a surface plate with a feeler gauge, and hole diameter is gauged with plug gauges rather than calipers because a punched hole is rarely perfectly round.

How Washer Thickness Affects the Joint

Thickness is not a cosmetic dimension. Under a preloaded bolt, the washer behaves as a spring in series with the joint, and a thin washer concentrates the clamp load into a small area directly under the nut. The DIN 125 thickness table exists because it represents the minimum thickness that will not deform under the proof load of the corresponding bolt class. Substituting a 1.0 mm washer where 1.6 mm is specified saves a few grams per piece and costs the joint its preload stability, particularly where the clamped material is aluminium or a thin-gauge steel panel.

The hole diameter matters as much as the thickness. A washer hole that is too large reduces the bearing area and lets the washer move under load; one that is too small will not pass over a bolt with a thread imperfection. ISO 7089 gives a hole tolerance that leaves a small clearance on a standard thread, which is the correct compromise. Buyers who specify “M12 washer, ID 12 mm” exactly are asking for an interference fit that will slow assembly and may not fit at all once the bolt is galvanized.

Applications

Flat washers from this range are used in structural steel bolting, machine assembly, automotive and trailer hardware, electrical enclosures and earthing plates, pipe supports, scaffolding, solar mounting systems, agricultural equipment and general maintenance. The pattern choice normally follows the joint: standard metric washers for machine assembly, hardened structural washers for steelwork, and fender washers wherever the clamped material is soft, slotted or thin.

Quality Assurance

• Coil grade and thickness verified on receipt; hardness checked on the first pressing of every run.
• Dimensional inspection every two hours: OD, ID, thickness and flatness, with results logged by lot.
• Hardness testing per lot on hardened grades; surface hardness plus a section check on F436 types.
• Coating thickness measured at five points per sample; salt spray to ASTM B117 available on request.
• Hydrogen bake records retained for hardened and electroplated washers.
• Visual inspection for burrs, cracks, laminations and die marks, with a defined AQL sampling plan.
• Third-party inspection and EN 10204 3.1 certification available on every shipment.

Corrosion Protection: Choosing the Right Coating

Washers corrode faster than the bolts they sit under, for a simple geometric reason: a washer is thin, so its edge-to-face ratio is high, and the edge is where a coating is thinnest and where water first attacks. Zinc plating at 5 to 8 µm is adequate for indoor and sheltered assemblies and is the cheapest option. For outdoor exposure, 12 µm of zinc with a trivalent passivation roughly doubles the time to red rust compared with a 5 µm coating, and it is usually worth the small premium.

Hot dip galvanizing at 40 to 80 µm is the correct choice for structural and outdoor work where the assembly cannot be repainted. Two details decide whether it actually works: the washers must be centrifuged after galvanizing so the hole is clear, and the coating must be thick on the edge, not just the face. A washer galvanized to 50 µm on the face and 15 µm on the edge will show edge rust within a season.

There is a compatibility rule that buyers often miss: mixing coating systems on the same joint creates a galvanic pair. A hot dip galvanized washer under a zinc plated bolt puts two different zinc thicknesses in contact with moisture between them, and the thinner coating fails first. Specify the same coating system across bolt, nut and washer, and the joint will age predictably instead of failing at the weakest component.

Packaging and Shipping

Washers ship in 25 kg double-wall cartons on ISPM 15 heat-treated pallets, stretch wrapped and strapped, or in counted poly bags where the customer’s line requires piece-level control. Each carton is labelled with standard, size, hardness, coating and lot number, and the pallet label repeats the heat number so that a receiving inspection can trace a carton to its coil without opening the pallet.

We ship FOB, CFR and CIF from Shanghai, Ningbo and Qingdao. Standard sizes are typically available in 15–25 days; hardened and hot dip galvanized lots need 25–35 days. Loading photographs, packing list and coating reports are issued with the shipping documents.

Request a Quotation

Tell us the standard or drawing, size, hardness, coating and quantity, and we will confirm the pattern dimensions, the hardness we will certify and the coating thickness range before quoting. If you are comparing suppliers, ask each one for the hardness and thickness values they will guarantee — those two numbers, not the price per thousand, decide whether the washer performs. Email our export team and receive a technical and commercial proposal within one working day.