DIN 1587 Domed Cap Nut Acorn Nut A4-80 Marine
DIN 1587 Domed Cap Nut (Acorn Nut) — A2-70 / A4-80 Stainless Steel, M6–M20
TheDIN 1587 domed cap nut — commonly called acorn nutorblind hex nut — is a standard hexagon nut with a closed, domed top that completely encloses the protruding bolt thread. On marine vessels, this design serves three critical functions: it eliminates the injury hazard of exposed sharp bolt ends on deck equipment and handrails, it shields the thread tip from salt spray to delay corrosion at the most vulnerable point, and it prevents mooring lines, fishing nets, or crew clothing from snagging on exposed threads.
sinofastener supplies DIN 1587 domed cap nuts in A2-70 (304 stainless steel)andA4-80 (316 stainless steel), covering sizes M6 through M20. Both variants are passivated after machining to restore the chromium oxide layer for sustained corrosion resistance in marine atmospheres and splash zones.
Why DIN 1587 Cap Nuts Matter on Ships
| Function | Description |
|---|---|
| Personnel Safety | Covers exposed bolt thread ends on handrails, stanchions, guard rails, and deck machinery — eliminates cuts and puncture injuries |
| Line Snag Prevention | Smooth domed surface prevents mooring lines, ropes, and nets from catching on sharp thread tips — critical on working decks and bollard areas |
| Thread-End Corrosion Shield | The closed dome blocks salt spray and moisture from reaching the bolt tip, where thread corrosion typically initiates first |
| Finished Appearance | Provides a clean, capped look on visible hardware — bridge equipment, companionway fittings, navigation light brackets |
A2-70 vs A4-80: Material Selection for Marine Environments
| Property | A2-70 (304) | A4-80 (316) |
|---|---|---|
| Standard | DIN 1587 / ISO 4032 (hex body) + domed cap per DIN 1587 form | |
| Tensile Strength | ≥ 700 MPa | ≥ 800 MPa |
| Molybdenum Content | None | 2.0–3.0% |
| Chloride Resistance | Suitable for sheltered / interior marine use | Required for exposed deck, splash zone, and offshore |
| Salt Spray Performance | Moderate — may show surface staining in continuous salt fog | Superior — resists pitting and crevice corrosion in chloride-rich atmospheres |
| Typical Marine Applications | Engine room panel guards, interior handrails, accommodation ladder hardware | Deck handrail stanchions, cleat mounting bolts, winch base brackets, exposed topside fittings |
| Passivation | Citric acid passivation per ASTM A967 | Citric acid passivation per ASTM A967 |
Where Domed Cap Nuts Are Used on Ships
- Deck Handrail Stanchions — acorn nuts on the top and base bolts prevent crew from catching clothing on exposed threads
- Cleat and Bollard Mounting — domed caps over foundation bolts prevent mooring line snag during berthing operations
- Winch Base Brackets — caps on anchor bolts eliminate trip hazards on working deck areas
- Navigation Light Brackets — finished appearance on visible mast and superstructure hardware
- Safety Barrier Posts — enclosed bolt ends on gangway and ladder guard rails
- Companionway Fittings — low-profile capped nuts on hatch and door frame hardware
DIN 1587 vs DIN 934 Hex Nut: When to Use Each
| Feature | DIN 1587 Domed Cap Nut | DIN 934 Hex Nut |
|---|---|---|
| Top Profile | Closed dome — covers bolt end completely | Open top — bolt thread protrudes |
| Safety Function | Eliminates exposed thread hazard | No thread-end protection |
| Height | Taller than standard hex nut (dome adds ~0.5×D) | Standard hex nut height per ISO 4032 |
| Space Constraint | Requires sufficient clearance above nut | Lower profile — suitable for tight clearance |
| Marine Use Case | Exposed hardware where crew contact or line snag is possible | General structural bolting where thread end is acceptable |
Available Sizes and Supply Information
| Size | A2-70 | A4-80 |
|---|---|---|
| M6 | ✓ | ✓ |
| M8 | ✓ | ✓ |
| M10 | ✓ | ✓ |
| M12 | ✓ | ✓ |
| M16 | ✓ | ✓ |
| M20 | ✓ | ✓ |
All DIN 1587 cap nuts are manufactured per the dimensional requirements of DIN 1587 (hexagon domed cap nuts). Material properties comply with ISO 898-2 (mechanical properties of fasteners). Thread tolerance per ISO 6H. All stainless steel variants undergo citric acid passivation per ASTM A967 before delivery.
sinofastener — 36 years of fastener manufacturing. Annual capacity 50,000 tonnes. Material certificates EN 10204 3.1 available. Third-party inspection (Lloyd's Register, DNV, Bureau Veritas) coordinated on request.
Material: A2-70 (304) / A4-80 (316) Stainless Steel
Standard: DIN 1587
Size Range: M6 – M20
Finish: Passivated per ASTM A967
Thread: Metric coarse, tolerance 6H
E-mail: sales@sinofastener.com | SINOFASTENER
