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FULLERKREG DIN 125A flat washers are manufactured from A4 stainless steel (SUS316) with a whitened and passivated surface finish. Conforming to DIN 125A, ISO 7089, and GB/T 97.1, these washers distribute bolt and nut bearing loads over a larger surface area, protect the joint surface from damage during tightening, and provide a superior corrosion-resistant bearing face for marine, chemical, and demanding industrial applications.
A4 (SUS316) stainless steel contains 2–3% molybdenum (Mo) in addition to chromium and nickel, giving it a significantly higher Pitting Resistance Equivalent Number (PREN ~24–26) compared to A2 SUS304 (PREN ~18–20). This makes A4 the preferred choice for marine, offshore, coastal, and chloride-containing environments where A2 may be insufficient. A4 washers are the standard pairing for A4 stainless bolts and nuts (DIN 931 / DIN 933 / DIN 934 A4).
| Standard | DIN 125A ≡ ISO 7089 ≡ GB/T 97.1 |
| Type | Plain flat washer — normal series (Form A), chamfer on one side of inner hole |
| Material | A4 Stainless Steel / SUS316 / 1.4401 |
| Surface Finish | Whitened & Passivated |
| Size Range | M3 – M36 |
| Hardness | ≤ 200 HV (per ISO 7089) |
| PREN (Pitting Resistance) | ~24–26 — significantly higher than A2 SUS304 (~18–20) |
| Corrosion Resistance | Excellent — superior to A2 in marine, chloride, and chemical environments |
| Magnetic | Slightly magnetic after cold working (stamping) |
| Recommended Pairing | A4 stainless bolts (DIN 931 / DIN 933 A4) and nuts (DIN 934 A4) for full material compatibility |
| Related Standard | ISO 7089 | GB/T 97.1 | DIN 125B (ISO 7090, double chamfer variant) |
| [Product Photo 1] | [Product Photo 2] | [Product Photo 3] | [Product Photo 4] |
All dimensions in millimeters (mm). Data per DIN 125A / ISO 7089 standard. Dimensions are identical for A2 and A4 grades.
| Nominal Size (Bolt d) | d1 — Inner Ø (mm) | d2 — Outer Ø (mm) | h — Thickness (mm) | Weight (kg / 1000 pcs) |
|---|---|---|---|---|
| M3 | 3.2 | 7 | 0.5 | 0.07 |
| M4 | 4.3 | 9 | 0.8 | 0.19 |
| M5 | 5.3 | 10 | 1.0 | 0.29 |
| M6 | 6.4 | 12 | 1.6 | 0.72 |
| M8 | 8.4 | 16 | 1.6 | 1.28 |
| M10 | 10.5 | 20 | 2.0 | 2.50 |
| M12 | 13.0 | 24 | 2.5 | 5.00 |
| M14 | 15.0 | 28 | 2.5 | 6.80 |
| M16 | 17.0 | 30 | 3.0 | 9.50 |
| M18 | 19.0 | 34 | 3.0 | 12.5 |
| M20 | 21.0 | 37 | 3.0 | 15.0 |
| M22 | 23.0 | 39 | 3.0 | 16.5 |
| M24 | 25.0 | 44 | 4.0 | 29.0 |
| M27 | 28.0 | 50 | 4.0 | 38.0 |
| M30 | 31.0 | 56 | 4.0 | 48.0 |
| M33 | 34.0 | 60 | 5.0 | 68.0 |
| M36 | 37.0 | 66 | 5.0 | 88.0 |
* d1 = inner diameter (clearance hole); d2 = outer diameter; h = nominal thickness. All dimensions per DIN 125A / ISO 7089. Weights are approximate based on A4 stainless steel density (7.98 g/cm³).
| Property | A4 — SUS316 (This Product) | A2 — SUS304 |
|---|---|---|
| Molybdenum (Mo) content | 2.0 – 3.0% | None |
| PREN (Pitting Resistance) | ~24–26 | ~18–20 |
| Chloride pitting resistance | Excellent | Good |
| Crevice corrosion resistance | Very good | Moderate |
| Marine / offshore suitability | Yes — preferred grade | Limited — may pit in high-chloride |
| Chemical processing | Excellent | Good |
| Food & pharmaceutical | Excellent | Good |
| Tensile strength (annealed) | ≥ 515 MPa | ≥ 500 MPa |
| Hardness | ≤ 200 HV | ≤ 200 HV |
| Density | 7.98 g/cm³ | 7.93 g/cm³ |
| Cost | Higher (Mo content) | Standard |
| Best for | Marine, offshore, chemical, high-chloride, pharmaceutical | General outdoor, food-grade, mild corrosive |
| Property | Value |
|---|---|
| Material Designation | A4 / SUS316 / 1.4401 / 0Cr17Ni12Mo2 |
| Chromium Content | 16.0 – 18.0% |
| Nickel Content | 10.0 – 14.0% |
| Molybdenum Content | 2.0 – 3.0% — key differentiator vs A2 |
| Tensile Strength | ≥ 515 MPa (annealed) |
| Hardness | ≤ 200 HV (per ISO 7089) |
| PREN | ~24–26 (vs ~18–20 for A2 SUS304) |
| Surface Finish | Whitened & Passivated |
| Corrosion Resistance | Excellent — superior chloride pitting and crevice corrosion resistance vs A2 |
| Temperature Range | −50°C to +300°C (continuous service) |
| Magnetic | Slightly magnetic after cold working (stamping process) |
| Density | 7.98 g/cm³ |
| Manufacturing Process | Cold stamped from A4 stainless steel strip |
Q: What is the difference between A4 and A2 stainless steel washers?
A: The key difference is molybdenum (Mo) content. A4 (SUS316) contains 2–3% Mo, which significantly improves resistance to chloride pitting and crevice corrosion — giving A4 a PREN of ~24–26 vs ~18–20 for A2 (SUS304). In practical terms, A4 is the preferred choice for marine, offshore, coastal, and chemical environments where A2 may suffer pitting corrosion. Dimensions are identical between A2 and A4 DIN 125A washers.
Q: What bolt sizes do these washers fit?
A: Each washer is sized by nominal bolt diameter. The inner diameter (d1) provides a clearance fit for the bolt shank. For example, an M12 washer has d1 = 13.0 mm (clearance for M12 bolt) and d2 = 24 mm outer diameter. Always match the washer nominal size to the bolt nominal size.
Q: Should I use A4 washers with A4 bolts?
A: Yes — always use matching material grades throughout the fastener assembly. Using A4 washers with A4 bolts and A4 nuts ensures full material compatibility, avoids galvanic corrosion between dissimilar metals, and maintains the corrosion resistance of the complete joint in marine and chemical environments.
Q: Are A4 stainless washers suitable for seawater immersion?
A: A4 (SUS316) provides significantly better resistance to seawater than A2 (SUS304) due to its molybdenum content. However, for continuous seawater immersion or subsea applications, even A4 can suffer crevice corrosion in stagnant conditions. For subsea or fully immersed applications, specify Duplex 2205 or Super Duplex stainless fasteners. A4 is excellent for splash zone, tidal, and above-waterline marine applications.
Q: What is the difference between DIN 125A and ISO 7089?
A: DIN 125A and ISO 7089 are equivalent standards with identical dimensions. DIN 125A is the German national standard; ISO 7089 is the international equivalent. GB/T 97.1 is the Chinese national standard with the same dimensions. FULLERKREG A4 washers conform to all three standards.
Q: Why are A4 stainless washers slightly magnetic?
A: A4 (SUS316) is an austenitic stainless steel that is non-magnetic in its annealed state. However, the cold stamping process used to manufacture washers induces a small amount of strain-induced martensite, making the finished washers slightly magnetic. This is normal and does not affect corrosion resistance or mechanical performance.
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