ISO 7089, 7090, 7091, 7092 & 7093 — the ISO Washer Standards Explained

Guide  ·  Updated June 2026

A drawing arrives with "ISO 7092" or a purchase order asks for "ISO 7090 M10." Buyers unfamiliar with the ISO numbering system often search for the DIN equivalent, find partial information, and either order the wrong part or send the supplier a spec that requires interpretation. The five ISO flat-washer standards — 7089, 7090, 7091, 7092 and 7093 — each encode three things: the outer-diameter series, the product (tolerance) grade, and the hardness class. Once those three variables are clear, mapping to a DIN equivalent is straightforward.

This guide covers each standard in turn. For the complete multi-system cross-reference table mapping DIN, ISO, ASME, GB and JIS numbers side by side, see the companion article: DIN, ISO & ASME Washer Standards: Cross-Reference & Equivalents →

ISO 7089 — normal series, plain face, grade A, 200 HV

ISO 7089 is the standard reference for a regular flat washer in the metric system. It specifies the normal outer-diameter series — the proportions that most people picture when they think "flat washer" — in product grade A (tight tolerances) at 200 HV hardness. There is no chamfer on either face.

Closest DIN equivalent: DIN 125 Form A. The nominal dimensions for each M-size are the same. If a drawing calls for ISO 7089, a washer produced to DIN 125 Form A satisfies the geometry and hardness requirement. HUIHUI MTCs reference both numbers on request. See DIN 125 flat washers →

ISO 7090 — normal series, chamfered face, grade A, 200 HV

ISO 7090 is ISO 7089 with one addition: a chamfer on one face. The chamfer is there to mate with the chamfer under a hex bolt or screw head, allowing the washer to seat flush rather than contact only at the corner. Outer diameter, inner bore and thickness are the same as ISO 7089 for a given M-size.

Closest DIN equivalent: DIN 125 Form B. DIN 125 defines both forms in the same document — Form A is the plain face (ISO 7089), Form B adds the chamfer (ISO 7090). In most general-purpose metric bolted joints the chamfer makes no practical difference, which is why Form A / ISO 7089 dominates stock. When a drawing specifically calls for ISO 7090, confirm with your supplier that the chamfered form is what ships — some suppliers stock only Form A.

ISO 7091 — normal series, grade C, typically 100 HV

ISO 7091 covers the same normal outer-diameter series as ISO 7089 but in product grade C — the coarser tolerance class. The bore and outer diameter are the same nominal values, but the manufacturing tolerances are wider and the hardness requirement is typically 100 HV rather than 200 HV. Grade C washers are generally produced by simpler stamping with less precise tooling and inspection.

Closest DIN equivalent: DIN 126. You will see ISO 7091 / DIN 126 specified for construction and building hardware where exact fit is not critical, and where cost is the driver. For mechanical assemblies, structural steel connections, or anywhere the joint sees significant load or vibration, specify ISO 7089 / DIN 125 Form A (grade A, 200 HV) instead.

ISO 7092 — small series, grade A, 200 HV

ISO 7092 specifies the small outer-diameter series. The outer diameter is smaller than the normal DIN 125 pattern — roughly 1.7–2× the bolt nominal rather than ~2–2.5×. The bore is the same clearance class. Use ISO 7092 where space is constrained: cap-screw counterbores, socket-head fasteners in counterbored holes, or anywhere the full standard OD would overhang the bearing surface or interfere with adjacent geometry.

Closest DIN equivalent: DIN 433. ISO 7092 and DIN 433 are dimensionally aligned; a supplier producing to DIN 433 is meeting ISO 7092. See HUIHUI DIN 433 / ISO 7092 small-OD washers → Note that small-OD washers carry lower stock volumes — confirm availability before specifying in large quantities.

ISO 7093 — large series, grade A, 200 HV

ISO 7093 (Part 1 covers the 200 HV hardness class) specifies the large outer-diameter series. The outer diameter is approximately three times the nominal bolt size — significantly wider than ISO 7089 / DIN 125. This larger bearing area distributes load over a greater surface, making ISO 7093 the correct choice for soft or compressible substrates (timber, plastics, composites, sheet metal), oversized clearance holes, or any joint where a standard washer would pull through or embed under load.

Closest DIN equivalent: DIN 9021. ISO 7093-1 and DIN 9021 are dimensionally equivalent. The part is also called a fender washer in trade. See HUIHUI DIN 9021 / ISO 7093 fender washers →

ISO 7094 — extra-large series (brief note)

ISO 7094 extends the series one step further with an extra-large outer diameter, used in specialist structural or seismic applications where even ISO 7093 / DIN 9021 is insufficient. It is not a standard stock item; most suppliers will produce to order. If ISO 7094 appears on a drawing, treat it as a custom order and supply the full dimension table to the manufacturer.

Three things the ISO number encodes: series, grade, hardness

Every ISO flat-washer standard number is shorthand for three independent variables. Mixing them up is how ordering errors happen.

1. Outer-diameter series

The series defines how large the washer OD is relative to the bolt. From smallest to largest: small series (ISO 7092 / DIN 433), normal series (ISO 7089/7090/7091 / DIN 125), large series (ISO 7093 / DIN 9021), extra-large series (ISO 7094). All four series are available in the same M-sizes. Two washers both fitting an M10 bolt can have very different ODs depending on which series is specified — always state the standard number, not just the bolt size.

2. Product grade (tolerance class)

Product grade is a manufacturing tolerance class, not a material quality rating. Grade A (ISO 7089, 7090, 7092, 7093) = fine tolerances on bore and OD, typical of precision stamping. Grade C (ISO 7091) = coarser tolerances, lower production cost, lower hardness. For export hardware, structural connections, and any drawing-specified application, grade A is the default.

3. Hardness class

The ISO plain-washer standards define two hardness classes: 200 HV (standard, for normal-strength fastener systems) and 300 HV (harder, for use with high-strength bolts — property class 8.8 and above in many assembly codes). For 304 and 316 stainless steel, 200 HV is the standard supply condition. Stainless cannot easily be hardened to 300 HV by standard production routes; if 300 HV is required with stainless, discuss with your supplier. Carbon steel washers for high-strength joints are typically heat-treated to reach the 300 HV class.

Quick-reference summary

For exact bore, OD and thickness dimensions for each M-size, refer to the published ISO specification or the supplier's production drawing. For the full cross-system mapping including ASME USS/SAE, GB and JIS, see our DIN, ISO & ASME Washer Standards cross-reference article. For HUIHUI product pages covering the most-ordered ISO-equivalent washers: DIN 125 / ISO 7089, DIN 9021 / ISO 7093, DIN 433 / ISO 7092.

FAQ