Silicon Bronze
Fasteners
Manufacturer India
Why Silicon Bronze — Contains No Zinc, So It Cannot Dezincify
Silicon bronze is a copper alloy strengthened primarily by silicon (2.8–3.8% Si) rather than tin (phosphor bronze) or zinc (brass). This single compositional fact — the absence of zinc — is the entire reason silicon bronze exists as a distinct engineering material: a fastener alloy that has all the corrosion resistance and appearance of a bronze, but zero risk of the dezincification failure mode that limits standard brass in continuous water contact.
Silicon bronze C65500 (“Everdur,” the trade name that has become generic in the marine trade) has been the standard fastener material for wooden boat hull construction for more than a century. Wooden boat builders specify silicon bronze for hull planking fasteners, keel bolts, stem and stern fastenings, and structural bronze hardware because: it does not dezincify in continuous bilge water or seawater contact; it has excellent atmospheric and marine corrosion resistance without the higher cost of Monel or exotic nickel alloys; it is readily weldable and brazeable for custom hardware fabrication; and — critically for wood boat construction — it does not react galvanically with the tannic acid in oak and other hardwoods the way steel or even some bronzes can, avoiding the black staining and localized corrosion known as “nail sickness.”
Compared with naval brass (C46400, tin-inhibited but still zinc-containing) and standard brass (C36000): silicon bronze contains no zinc at all — there is no dezincification mechanism possible, regardless of water stagnancy, temperature, or pH. This makes silicon bronze the correct specification for permanent submerged and below-waterline marine fasteners where naval brass’s tin inhibitor still carries residual risk over multi-decade service life, and where phosphor bronze’s higher cost is not justified by application-specific anti-galling requirements.
| Property | Value |
|---|---|
| Cu | 94.0–96.0% |
| Si | 2.8–3.8% |
| Mn (residual) | 0.5–1.3% |
| Zn | 0% — None |
| Min UTS (annealed) | ≥380 MPa |
| UTS (half-hard) | ≥450 MPa |
| Non-Magnetic | Yes |
| Weldable / Brazeable | Excellent |
| Colour | Reddish-Gold Bronze |
Why Silicon Bronze — The Wooden Boat Building Standard
No Dezincification — Ever, Regardless of Service Life
Silicon bronze’s total absence of zinc makes dezincification chemically impossible — not “resistant,” but categorically excluded as a failure mode. For hull fasteners with 30–50 year service expectations below the waterline, this is the deciding factor over DZR brass, which relies on an arsenic inhibitor that provides resistance but not the absolute immunity of a zinc-free alloy. Where a wooden boat’s structural integrity depends on fastener survival for decades, silicon bronze removes the failure mode entirely rather than merely inhibiting it.
No “Nail Sickness” — Compatible with Tannic Hardwoods
Oak, chestnut, and other tannin-rich hardwoods used in traditional boat building can cause accelerated galvanic corrosion of embedded iron and steel fasteners — a phenomenon called “nail sickness” that stains the wood black and progressively weakens the fastener. Silicon bronze does not react with wood tannins the way ferrous fasteners do, making it the traditional and still-current standard for oak-hulled, teak-decked, and other tannin-bearing timber boat construction where fastener-wood chemical compatibility over decades is essential.
Weldable and Brazeable — Custom Marine Hardware Fabrication
Silicon bronze is readily weldable (with silicon bronze filler rod, which is also the standard TIG/gas welding filler for joining bronze, brass, and copper to steel) and brazeable, making it the material of choice for boatyards and restoration shops fabricating custom hardware, repairing castings, and joining dissimilar bronze fittings. The same alloy used as fastener stock (C65500) is also produced as MIG/TIG welding wire — a boatyard can weld a bronze fitting using filler rod from the same alloy family as the fasteners holding it in place.
Heritage-Correct Appearance for Restoration Work
Silicon bronze develops an attractive brown-green patina similar to traditional bronze and brass hardware, making it the correct material for historically accurate restoration of period boats, heritage buildings, and antique furniture hardware where the fastener’s visible appearance and patina development must match original period bronze fittings. Unlike stainless steel (which looks obviously modern) or plated steel (which will eventually corrode and stain), silicon bronze ages authentically and matches the surrounding original bronze hardware.
Grade Profiles — C65500 (Everdur) vs C65100 (Low Silicon Bronze)
C65500 is the primary marine and boat-building grade — higher strength, higher silicon. C65100 is a lower-silicon, more ductile variant used where cold formability is prioritised over maximum strength.
C65500 (Everdur)
C65100 (Low Silicon Bronze)
Silicon Bronze Fastener Types — Full Range
C65500 (Everdur) is the primary stocking grade for marine and structural fasteners. C65100 available on order for cold-formed components. M4–M24.
Carriage Bolts
Round head square neck carriage bolts in C65500. M6–M20. The signature silicon bronze fastener for wooden boat hull planking — the square neck self-locks into the wood without a separate anti-rotation feature, and the round head sits flush and smooth against the exterior hull surface. The standard fastener for traditional and classic wooden boat construction worldwide.
Hex Bolts
Full thread and partial thread hex bolts in C65500. M4–M24. Marine structural connections, keel bolt assemblies, boatyard hardware fabrication, architectural bronze installations, and heritage restoration hex bolts matching period-correct bronze finish and patina development for historically accurate repair work.
Hex Nuts
Standard hex nuts in C65500 and C65100. M4–M24. Matched from same ASTM B98-certified rod as hex bolts and carriage bolts. Keel bolt nut sets, structural bronze nut assemblies, and marine below-waterline nut fastenings where the zero-zinc composition of the mating nut is as important as the bolt for total system dezincification immunity.
Washers
Plain flat washers in C65500. M4–M24. For complete silicon bronze fastener assembly documentation — bolt, nut, and washer from the same certified rod. Keel bolt washer plates, hull planking bolt washers, and all below-waterline marine assembly sets requiring uniform zero-zinc bronze across every wetted-surface component.
Threaded Rods / Keel Bolts
Full thread threaded rods in C65500, purpose-cut and threaded to length for keel bolt applications. M10–M24, lengths to 1,500mm. The traditional wooden boat keel bolt material — silicon bronze keel bolts have decades-long proven service records securing lead or iron keel castings to wooden hull structures below the waterline.
Wood Screws & Machine Screws
Slotted and Phillips wood screws (DIN 96 style) and machine screws in C65500. M3–M12. Deck hardware attachment screws, hull planking fastening screws, cabin joinery screws, and all traditional wooden boat construction screw applications where silicon bronze’s wood-compatibility and zero-dezincification properties are required at screw scale.
Custom Silicon Bronze
Non-standard head forms, restoration-matched thread pitches, custom carriage bolt lengths, deck plates, and any drawing-specific silicon bronze fastener configuration for boat building, architectural bronze, or heritage restoration projects. Contact sales@akbarfasteners.in with grade, drawing, and quantity.
Silicon Bronze Application Areas
Wooden boat building, marine below-waterline hardware, welding filler applications, and heritage restoration — the four application niches where silicon bronze is the uniquely correct copper alloy.
Wooden Boat Building
keel bolt assemblies
Marine Below-Waterline
bilge hardware fastenings
Welding Filler Rod
bronze-to-steel joining
Heritage Restoration
historic hardware repair
Architectural Bronze
decorative bronze fixtures
Cabinetry & Furniture
antique furniture screws
Statuary & Art Bronze
public art installation bolts
Composite Hull Bolting
bronze backing plate hardware
Silicon Bronze Standards Coverage
Same ISO 9001:2015 quality system as our complete fastener range. PMI confirms Si content and — critically — zero Zn presence, distinguishing genuine silicon bronze from brass which can appear visually similar.
Complete Documentation Package
ASTM B98 Stated
Conformance
Zero Zn Verified
Annealed / Half-Hard
Tensile · Hardness
Related Copper Family Fastener Alloys
Silicon bronze for zero-dezincification marine and heritage work. Aluminium bronze for higher-strength marine structural. Phosphor bronze for anti-galling springs. Brass for cost-sensitive indoor work.
Aluminium Bronze Fasteners
When silicon bronze’s ≥380 MPa strength is insufficient for high-load marine structural connections — aluminium bronze C63000 (≥760 MPa) is the correct upgrade for keel bolts on larger vessels, propeller shaft hardware, and high-strength marine structural bolting beyond silicon bronze’s capability.
View Al-Bronze →Phosphor Bronze Fasteners
When anti-galling thread behaviour for repeated disassembly is the primary requirement rather than dezincification immunity — phosphor bronze’s copper phosphide precipitates prevent thread cold-welding in a way silicon bronze does not specifically address. For valve gland bolts and bearing retention screws.
View Ph.Bronze →Brass Fasteners
For indoor, dry, non-marine applications where machinability and cost are the primary drivers — C36000’s 100% machinability rating and lower cost make it correct for instrument and general hardware where silicon bronze’s marine-grade dezincification immunity is not required.
View Brass Range →Copper Nickel Fasteners
For seawater piping system galvanic compatibility and biofouling resistance that silicon bronze does not specifically provide — when the piping system is Cu-Ni, matching fasteners maintain system alloy compatibility at the flange face.
View Cu-Ni Range →Need Silicon Bronze
Fasteners?
Grade (C65500/C65100) · form (carriage bolt/hex/keel bolt) · size · quantity. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Export: +91 8696 32 4646 · Support: +91 800 9315 333 · export@akbarfasteners.in