Plain washer standards compared: DIN 125, ISO 7089, ISO 7090, DIN 433 and ASME B18.21.1 Type A/B
These six designations all describe the same kind of part — a flat annulus that spreads bolt load — but they belong to two dimensioning systems and carry different series structures, edge forms and hardness pairings. This table compares the plain-washer standards we publish individual specification pages for, using only fields that mean the same thing across the columns. Where a figure is not established by the collected evidence, the cell says so and asks you to confirm it at RFQ; nothing is filled in with an assumption, and no cell implies a standard cannot be supplied.
Comparison table
The worked-row row quotes each column at its own collected example size — metric at M10, the ASME columns at their printed example rows — so those figures position the systems, they are not convertible numbers.
| Field | DIN 125 (Form A/B) | ISO 7089 | ISO 7090 | DIN 433 (Small OD) | ASME Type A | ASME Type B |
|---|---|---|---|---|---|---|
| Standard & series | DIN 125 Form A/B — plain washers for hex bolts and nuts, the default metric bearing washer | ISO 7089 — plain washers, normal series, product grade A, unchamfered | ISO 7090 — plain washers, chamfered, normal series, product grade A | DIN 433 — small outer diameter flat washers, the metric reduced series | ASME B18.21.1 Type A — plain washers, inch series, narrow / regular / wide per size as printed | ASME B18.21.1 Type B — plain washers, inch series, narrow / regular / wide on every nominal size |
| International counterpart The field that maps the two systems: which metric and inch designations describe the same part family — and where no counterpart is printed. | ISO 7089 counterpart — Form A is the unchamfered form, Form B the chamfered one (matching ISO 7089 vs 7090) | DIN 125 Type A counterpart — same hole/OD/thickness series, unchamfered edge | DIN 125 Type B counterpart — same hole/OD/thickness series, chamfered outer edge | ISO 7092 counterpart — the international reduced-series designation for the same small-OD washer | Inch-system document — no ISO counterpart printed; the metric plain washers on this site follow ISO 7089 as a separate system | Inch-system document — Type A is its sibling table under the same ASME B18.21.1; no ISO counterpart printed |
| Distinguishing geometry | Flat annulus in two forms — chamfered Form A as the standard series, unchamfered Form B as the counterpart | Unchamfered (straight-edged) outer profile — seats under flat-faced components with no fillet-bearing issue | Chamfered outer edge — lets a hex head or nut fillet run out on the chamfer instead of bridging a sharp edge | Noticeably reduced outer diameter for the same hole — 18 mm instead of 21 mm OD at M10, 39 mm instead of 44 mm at M24 in the collected worked rows | Flat annulus with three series per size group — narrow, regular and wide; the same bolt size takes all three (source flags the series split as a table footnote) | Flat annulus with all three series on every size from No.0 up — the series decision exists from the smallest screw sizes (flagged anti-coin ODs on selected rows) |
| Size range (collected) | Shares the ISO 7089/7090 dimension set on the collected manufacturer sheets — M3 to M72 | M3 to M72 in the collected dimension series (metric normal series) | M3 to M72 in the collected dimension series (metric normal series) | M1 to M36 in the collected dimension series (metric reduced series); stocked M1.5–M20 in A2/A4 stainless | Nominal bolt sizes 0.072 – 4 in, 40 printed rows across the narrow/regular/wide series | Nominal washer sizes No.0 – 2 in, 84 printed rows (28 sizes × 3 series) |
| Worked row (as published) Same meaning (one printed dimension row) but different bases — metric columns quote M10, the ASME columns quote their own collected example rows; figures are marked, not converted. | M10: 20 mm outer diameter × 10.5 mm inner diameter — about 228 mm² bearing area | M10: 10.5 mm hole × 21 mm outer diameter × 2 mm thick | M10: 10.5 mm hole × 21 mm outer diameter × 2 mm thick (chamfer is a form feature, not a dimension change) | M10: 10.5 mm hole × 18 mm outer diameter × 1.6 mm thick (vs 21 mm OD in the normal series) | 1/2 in regular series: ID limits 0.531/0.515 in, OD 1.000/0.969 in, thickness 0.095/0.080 in — max/min per row | 1/4 in regular series: ID 0.281 in (+0.015/−0.005), OD 1.000 in, thickness 0.063 in — basic with plus/minus tolerance (the 0.734 in OD of the narrow series carries the source anti-coin flag) |
| Hardness & material pairing | 200 HV hardness class — dimensioned for assemblies up to property class 8.8; 10.9/12.9 joints need a hardened washer instead | 200 HV-class plain washer serving assemblies up to class 8.8; stainless A2/A4 classes 50/70/80 (500/700/800 N/mm²) on the collected strength table | Stainless A2/A4 austenitic classes 50 (to M39), 70 (to M20), 80 (to M20) — 500/700/800 N/mm²; steel, brass, aluminum and nylon also on the collected material list | Collected stock statement M1.5–M20 in A2 and marine-grade A4 stainless; same A2/A4 strength-class table as the ISO series | Not tabulated by the collected chart — material, hardness range and finish per RFQ Unverified — confirm at RFQ | Not tabulated by the collected chart — material, hardness range and finish per RFQ Unverified — confirm at RFQ |
| Best for | The default metric bearing washer for ordinary bolted joints through clearance holes — steel, stainless and brass builds up to class 8.8 | General load distribution on flat mating faces — under plain nuts, set faces, brackets and housings where no fillet bears on the washer | The same bearing job under a filleted hex head or nut — where the chamfer keeps the fillet from bridging the edge and cutting preload | Clustered bolt patterns and confined bearing faces — where full-size washers would overlap edges or foul adjacent geometry | Inch-series joints sized 0.072–4 in — order the narrow/regular/wide series explicitly as a bearing-area decision | Small inch screws up to 2 in where the series choice matters from No.0 — narrow, regular and wide printed on every size |
- Verified
- Differs
- Unverified — confirm at RFQ
- Conditional — confirm configuration
How to choose
By which system your drawing speaks
If the drawing or the mating parts are metric, you are in the DIN/ISO column group — and inside it the first fact to hold on to is that DIN 125, ISO 7089 and ISO 7090 share one hole, outer-diameter and thickness set: the choice among them is a form choice (chamfered under a filleted hex head or nut, unchamfered under a flat face), not a fit choice. If the drawing is inch, you are in the ASME B18.21.1 system, where the equivalent decision is the series — narrow, regular or wide — printed right on the chart. The two systems are crossed only at the printed limits, not by converting a nominal size.
By the bearing area you actually have
All six designations let you trade footprint against bearing area. The metric reduced series (DIN 433 / ISO 7092) trims the outer diameter for clustered patterns and confined faces; the inch wide series does the opposite, spreading load over soft or thin substrates and bridging oversized holes. Regular or normal is the default in both systems — depart from it when the geometry, not the load, forces your hand, and order the series explicitly, because the same bolt size takes several of them.
By what the washer must withstand
Hardness pairing is where the systems read differently. The collected metric sheets print it: a 200 HV-class plain washer serves assemblies up to property class 8.8, and the stainless tables publish the 50/70/80 strength classes. The collected ASME charts are geometry-only — material, hardness range and finish are RFQ lines, which is a reading of the collected sources, not a limit on supply. Against property class 10.9 or 12.9 bolts in either system, a hardened washer is the correct part, and that is a different product line from every column in this table.
Frequently asked questions
DIN 125, ISO 7089 and ISO 7090 — are they interchangeable?
For fit, yes: the collected sheets give one hole, outer-diameter and thickness set shared across the DIN 125 / ISO 7089 / ISO 7090 designations — the M10 washer is 10.5 × 21 × 2 mm whichever of the three you order. What differs is form and edge: ISO 7089 (DIN 125 Type A) is the unchamfered form, ISO 7090 (DIN 125 Type B) carries a chamfered outer edge so a filleted hex head or nut seats flat instead of bridging a sharp edge. So the choice inside the metric normal series is driven by what sits on top of the washer, not by the hole it covers. Where a drawing names one designation, quote against it; where it says only "flat washer, M10", state the form (chamfered or not) on the RFQ.
Can I substitute an inch ASME washer for a metric one, or the other way round?
Not by name conversion. The ASME B18.21.1 tables are dimensioned in inches with their own series structure — narrow, regular and wide — and the two systems size their holes differently (a metric washer takes its hole from the thread clearance series, e.g. 10.5 mm at M10; an inch washer from the printed ID limits, e.g. 0.531/0.515 in at 1/2 in). The honest way to cross the systems is at the printed limits: take the hole and outer diameter your joint actually needs and check them against each page's own dimension table rather than converting a nominal size. The collected ASME charts tabulate geometry only — hardness, finish and material are per RFQ — so state those alongside when the substitution is load-bearing.
Which series should I order — normal, reduced, narrow, regular or wide?
It is a bearing-area decision, and both systems expect you to make it explicitly. In the metric series, the normal series (DIN 125 / ISO 7089 / ISO 7090) is the default; the reduced DIN 433 / ISO 7092 series earns its place where clustered bolt patterns would overlap full-size washers or where the bearing face is too small to carry the normal OD. In the inch system, regular is the default under a hex or socket bearing face, narrow buys clearance or weight, and wide spreads load on soft or thin substrates — ASME Type B prints all three series on every size from No.0, while Type A splits the series on the larger sizes. Either way, "a washer for an M10 / a 1/2 in bolt" leaves the most consequential dimension undefined: name the series and the form on the RFQ.
Individual washer specification pages
Each standard has its own page — dimension tables, hardness pairings and RFQ guidance. For washers compared by what they do rather than by standard, see the washer type comparison.
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