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FULLERKREG DIN 9021 Hot Dip Galvanised fender washers are manufactured from low carbon steel with a hot dip galvanised (HDG) zinc coating per ISO 10684. DIN 9021 specifies a large outer diameter washer — the outer diameter (d2) is approximately 3× the bolt nominal diameter — providing a significantly larger bearing area than standard DIN 125A washers to prevent pull-through and embedment in soft or thin materials such as timber, plywood, and composite panels.
The HDG coating (45–85 μm zinc per ISO 10684) provides the highest level of corrosion protection available for carbon steel washers — approximately 10× thicker than electroplated zinc — delivering 20–50+ years of outdoor corrosion protection. The metallurgically bonded zinc-iron alloy coating provides both barrier and cathodic (sacrificial) protection, making these washers the preferred choice for long-term outdoor structural timber, civil engineering, and infrastructure applications.
Note: Due to the thick HDG coating (45–85 μm per side), HDG washers have slightly larger effective dimensions than nominal DIN 9021 values. Use HDG oversize nuts with HDG bolts and washers. Verify clearance fit before assembly.
| Standard | DIN 9021 (dimensions) | ISO 10684 (HDG coating) |
| Type | Large outer diameter (fender / penny) washer — plain flat, no chamfer |
| Material | Low Carbon Steel (mild steel) |
| Surface Finish | Hot Dip Galvanised (HDG) — per ISO 10684 |
| Zinc Coating Thickness | 45 – 85 μm (per ISO 10684) |
| Salt Spray Resistance | ≥ 1000 hours to red rust (typical for 45–85 μm HDG) |
| Outdoor Service Life | 20 – 50+ years (environment-dependent, per ISO 14713) |
| Size Range | M6 – M24 |
| OD Ratio | Outer diameter ≈ 3× nominal bolt diameter (vs ~2× for DIN 125A) |
| Recommended Bolt Grade | Grade 4.6, 4.8, 5.6, 6.8 | HDG bolts (DIN 931 / DIN 933 HDG) |
| Corrosion Resistance | Excellent — best-in-class for carbon steel; 20–50+ year outdoor service life |
| Magnetic | Yes |
| Related Standard | ISO 10684 (HDG fasteners) | ISO 14713 (zinc coating durability) | ISO 7093 (large washer) |
| [Product Photo 1] | [Product Photo 2] | [Product Photo 3] | [Product Photo 4] |
All dimensions in millimeters (mm). Nominal dimensions per DIN 9021 (pre-coating). HDG coating (45–85 μm per surface) adds approximately 0.09–0.17 mm to each radius — verify clearance fit before assembly.
| Nominal Size (Bolt d) | d1 — Inner Ø (mm) | d2 — Outer Ø (mm) | h — Thickness (mm) | Weight (kg / 1000 pcs) |
|---|---|---|---|---|
| M6 | 6.4 | 18 | 1.6 | 1.93 |
| M8 | 8.4 | 24 | 2.0 | 4.29 |
| M10 | 10.5 | 30 | 2.5 | 8.29 |
| M12 | 13.0 | 37 | 3.0 | 14.8 |
| M14 | 15.0 | 44 | 3.0 | 20.7 |
| M16 | 17.0 | 50 | 3.0 | 26.7 |
| M20 | 21.0 | 60 | 4.0 | 52.3 |
| M24 | 25.0 | 72 | 4.0 | 75.1 |
* Nominal dimensions per DIN 9021 (pre-coating). HDG coating adds ~0.09–0.17 mm per radius. Weights are approximate based on low carbon steel density (7.85 g/cm³) excluding zinc coating. HDG starts from M6 due to coating thickness constraints on smaller sizes.
| Property | DIN 9021 HDG (This Product) | DIN 125A HDG (Standard OD) |
|---|---|---|
| Outer diameter ratio | ~3× bolt diameter | ~2× bolt diameter |
| M12 outer diameter | 37 mm | 24 mm |
| Bearing area (M12) | ~940 mm² | ~320 mm² (~3× smaller) |
| Pull-through resistance | High — for timber, plywood, soft materials | Standard — for hard structural materials |
| Zinc coating | HDG 45–85 μm (ISO 10684) | HDG 45–85 μm (ISO 10684) |
| Outdoor service life | 20–50+ years | 20–50+ years |
| Best for | Timber framing, decking, plywood, thin sheet — long-term outdoor | Steel, concrete structural — long-term outdoor |
| Property | HDG Carbon Steel (This Product) | Zinc CR3 Carbon Steel | A4 Stainless (SUS316) |
|---|---|---|---|
| Zinc coating thickness | 45 – 85 μm | 5 – 8 μm | N/A (passive film) |
| Salt spray resistance | ≥ 1000 hours | ≥ 240 hours | Excellent (no zinc) |
| Outdoor service life | 20 – 50+ years | 3 – 10 years | 20–50+ years |
| ACQ/CCA treated timber | Good (HDG recommended) | Not recommended | A4 preferred |
| Marine / high-chloride | Good (above waterline) | Limited | Excellent |
| Cost | Low–medium | Low | High |
| Best for | Long-term outdoor structural timber, civil engineering | General outdoor, short-medium term | Marine, coastal, treated timber |
| Property | Value |
|---|---|
| Base Material | Low Carbon Steel (mild steel, ≤ 0.25% C) |
| Yield Strength | ≥ 235 MPa (typical for low carbon steel) |
| Tensile Strength | 370 – 500 MPa |
| Surface Finish | Hot Dip Galvanised (HDG) per ISO 10684 |
| Zinc Coating Thickness | 45 – 85 μm (per ISO 10684) |
| Zinc Purity | ≥ 98.5% Zn (molten zinc bath) |
| Coating Bond | Metallurgical Zn-Fe alloy bond — cannot be peeled or chipped |
| Salt Spray Resistance | ≥ 1000 hours to red rust (typical) |
| Outdoor Service Life | 20–50+ years (per ISO 14713, environment-dependent) |
| Temperature Limit | Up to +200°C (HDG service limit) |
| Magnetic | Yes |
| Density (steel) | 7.85 g/cm³ |
Q: What is the difference between DIN 9021 HDG and DIN 125A HDG?
A: Both use the same HDG coating (45–85 μm, ISO 10684) and low carbon steel base material. The difference is the outer diameter: DIN 9021 has d2 ≈ 3× bolt diameter (e.g. M12: 37 mm) vs DIN 125A d2 ≈ 2× bolt diameter (e.g. M12: 24 mm) — approximately 3× greater bearing area. Choose DIN 9021 when fastening into timber, plywood, or thin materials where pull-through is a concern; choose DIN 125A for steel-to-steel or concrete structural connections.
Q: Should I use HDG or A4 stainless DIN 9021 washers for outdoor timber?
A: Both are suitable for long-term outdoor timber applications. HDG carbon steel is the more cost-effective choice for general outdoor structural timber (20–50+ year service life). A4 stainless is preferred for: marine or coastal environments with high salt-air exposure; ACQ/CCA treated timber (preservative chemicals can attack HDG zinc over time); and applications where the washer will be visible and appearance matters. Contact FULLERKREG if you need guidance on material selection for your specific application.
Q: Why does HDG start from M6 rather than M5?
A: The thick HDG coating (45–85 μm per surface) significantly reduces the inner diameter clearance of small washers. For M5 washers, the coating thickness relative to the inner diameter is too large to maintain reliable clearance fit with the bolt shank after galvanising. HDG is therefore practical from M6 upwards for DIN 9021 washers.
Q: Do I need to use HDG nuts with HDG washers and bolts?
A: Yes. HDG bolts are supplied with oversize-tapped nuts to accommodate the zinc coating on the bolt threads. Standard nuts will not fit HDG bolts. For a complete HDG fastener assembly, specify HDG bolts, HDG oversize nuts, and HDG washers together.
Q: What is the ISO equivalent of DIN 9021?
A: DIN 9021 is equivalent to ISO 7093 (large washer series). Both specify a large outer diameter washer with d2 ≈ 3× bolt diameter. DIN 9021 is the German national standard; ISO 7093 is the international equivalent.
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