Washer types compared: plain, fender, spring lock, hardened, USS and SAE
A washer is specified by the job its bearing face has to do: spread a clamp load, span an oversized hole, add locking friction, or transfer structural load without embedding. This table compares the six washer types 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 type cannot be supplied.
Comparison table
Metric DIN patterns and inch-series ASME patterns are tabulated side by side for procurement orientation — a substitution between the two families should be confirmed against the drawing (the metric counterparts are named in each column's own page).
| Field | DIN 125 Plain Flat | DIN 9021 Fender (Large OD) | DIN 127 Spring Lock | ASTM F436 Hardened | USS Flat (Inch) | SAE Flat (Inch) |
|---|---|---|---|---|---|---|
| Standard & type | DIN 125 Form A/B — plain flat washer for hex bolts/nuts (ISO 7089 counterpart) | DIN 9021 — large-series flat washer, "fender" pattern (ISO 7093 counterpart) | DIN 127 — helical spring lock washer, split type (ASME B18.21.1 inch counterpart) | ASTM F436 — hardened steel washer, inch series (F436M metric counterpart) | ASME B18.21.1 inch-series plain washer, legacy USS wide-body series | ASME B18.21.1 inch-series plain washer, legacy SAE narrow-body series |
| Primary function Differs in kind across the columns: load distribution (plain patterns), friction/spring locking (split type), or structural-grade load transfer (hardened). | Distributes clamp load; gives the nut or head a true bearing face | Large OD spreads bearing load over weak, slotted or oversized holes | Differs in kind — flattens under tightening; split edges bite nut and joint faces, spring action resists back-off | Structural load transfer — hardened so the bolt stretches before the washer deforms | Bearing area for load distribution — wider and thicker than SAE at the same bolt size | Bearing fit in tight clearances — narrower and thinner than USS at the same bolt size |
| Hardness / strength class Same meaning across columns (resistance to embedment under the bolt load); the bases differ — HV class vs HRC — and are marked, not converted. | 200 HV — dimensioned for assemblies up to property class 8.8 | 200 HV series — assemblies up to property class 8.8; hardened equivalents above | Spring steel (no hardness class tabulated on the collected page; confirm at RFQ) Unverified — confirm at RFQ | Type 1 carbon steel, quenched and tempered, HRC 38–45 (different scale from the 200 HV class — not converted) | Unverified — the collected page does not state a hardness class; confirm at RFQ Unverified — confirm at RFQ | Unverified — the collected page does not state a hardness class; confirm at RFQ Unverified — confirm at RFQ |
| Required / paired with | General joints through clearance holes; class 10.9/12.9 joints call for a hardened washer instead | Step up from DIN 125 over slotted holes or soft sheet | DIN 7980 high-collar variant exists for use under socket head cap screws | Required with F3125 A325/A490 structural connections; mandatory over slotted/oversized holes and turn-of-nut tensioning | Inch-series joints needing bearing area: oversized holes or soft substrate | Inch hardware where clearance around the fastener is tight |
| Example dimensions Each column quotes its own collected anchor size — the sizes differ by column and are NOT comparable numbers; they show the pattern's proportions, nothing else. | At M10: 20 mm OD × 10.5 mm ID (≈ 228 mm² bearing area) | Unverified — no single anchor size quoted on the collected page; dimension table on request Unverified — confirm at RFQ | Unverified — no single anchor size quoted on the collected page; dimension table on request Unverified — confirm at RFQ | Unverified — geometry note only: smaller OD than common flat washers by design, to fit clustered bolt patterns Unverified — confirm at RFQ | At 1/2": ID 0.562 in × OD 1.375 in × 0.086–0.132 in thick | At 1/4": ID 0.281 in × OD 0.625 in × 0.051–0.080 in thick |
| Typical service | General bolted joints in steel, stainless and brass builds | Slotted or oversized holes, thin sheet, plastics and soft substrates, body and fender work | Slight to moderate vibration: motor mounts, small machinery, appliances, automotive | Structural steel connections with A325/A490 bolts | General inch hardware where bearing area matters | Compact inch assemblies |
- Verified
- Differs
- Unverified — confirm at RFQ
- Conditional — confirm configuration
How to choose
By the bearing problem
Ordinary joints take the plain flat washer — it distributes the clamp load and gives the head a true face. When the hole is slotted or oversized or the substrate is thin and soft, the fender pattern's large outer diameter is the tool; in the inch series the same job splits into USS (wide body, more bearing area) versus SAE (narrow body, tight clearances). Hardened F436 washers are not a fourth plain washer — they exist so the bolt stretches before the washer embeds.
By strength class
The 200 HV class pairs DIN 125 and DIN 9021 with assemblies up to property class 8.8; class 10.9 and 12.9 joints call for a hardened washer instead. F436 runs HRC 38–45 quenched and tempered — a different scale and a different job from the 200 HV class, which is why the table marks the difference rather than converting it.
By the locking duty
The spring lock washer is the only type in this table whose function is friction, not bearing: it suits slight-to-moderate vibration service, and the DIN 7980 high-collar variant is the version made to sit under socket head cap screws. Where loosening is critical, pair the washer decision with a prevailing-torque lock nut — the nut pairing comparison covers that side of the joint.
Frequently asked questions
Do spring lock washers actually prevent loosening?
They are one locking aid among several, suited to slight-to-moderate vibration: the split coil flattens under tightening and its edges bite both faces, adding friction against back-off. For joints where loosening is critical, a prevailing-torque lock nut or a thread-locking approach does the job the washer cannot — the washer-types knowledge guide compares the methods.
When does a joint require a hardened (F436) washer?
Structural connections built with F3125 A325/A490 bolts require them, and they are mandatory over slotted or oversized holes and under turn-of-nut tensioning, where a soft 200 HV washer would embed and lose preload. The principle: the washer must be stronger than the bolt yield, so the bolt stretches before the washer deforms.
USS or SAE — which flat washer do I order?
Both are inch-series plain washers per ASME B18.21.1; the difference is the body. USS is wider and thicker at the same bolt size — more bearing area for oversized holes and soft substrates. SAE is narrower and thinner, made to fit tighter clearances. Match the metric side with DIN 125, or step to DIN 9021 fender pattern when bearing spread matters more than the outline.
Individual washer specification pages
Each type has its own page — dimension series, class pairing and RFQ guidance.
- DIN 125 Plain Flat
- DIN 9021 Fender (Large OD)
- DIN 127 Spring Lock
- ASTM F436 Hardened
- USS Flat (Inch)
- SAE Flat (Inch)
The full function-and-selection mechanics: Washer types, function and selection
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- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
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