This tool is currently in beta. The finish data, corrosion resistance values, and engineering guidance presented here are based on published standards and SBS field experience, but are being actively reviewed and refined.
We encourage you to use this tool and share your feedback with the SBS engineering team. If you notice missing finishes, data discrepancies, or have suggestions, please reach out directly so we can improve it for everyone.
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- Indoor / dry: Minimal protection needed. Zinc clear or black oxide often sufficient.
- High humidity / mild outdoor: Zinc clear or yellow trivalent with sealant (96+ hr salt spray).
- Automotive / under-hood: Zinc Nickel or Geomet 321. Must survive thermal cycling.
- Marine / severe corrosion: Geomet 720+, Zinc Nickel 12ES, or stainless with passivation.
- Chemical / acid exposure: Consult SBS engineering. Organic coatings or speciality platings required.
- Low-carbon steel: All zinc electroplate options applicable. HE risk managed by baking.
- High-hardness / PC 10.9, 12.9: Avoid standard zinc electroplate. Use Geomet 321, Zinc-Tin, or mechanical zinc (no HE risk).
- Case-hardened tapping screws: Geomet 321 + ML preferred to prevent cold welding.
- Stainless steel: Passivation standard. Electropolish for galling risk. RIE 4037A for black aesthetic.
- Aluminum: Anodize. Never apply zinc electroplate directly to aluminum.
- RoHS / ELV (automotive, EU): Eliminates all Cr6 (hexavalent) finishes. Use trivalent (Cr3) or non-chrome alternatives only.
- REACH / SVHC: Cadmium and hexavalent chrome are SVHC. Avoid entirely unless military exemption applies.
- Torque-tension spec (K-factor): Dry film lubricants and topcoats (Geomet PLUS ML/VL) give tighter CoF range. Specify CoF target in callout.
- Food / medical / NSF: Consult SBS for FDA-compliant coating options.
- HE occurs during: Acid pre-treatment (pickling) and electroplating. Atomic hydrogen diffuses into steel lattice.
- Most susceptible: Steels above 39 HRC (approx. Grade 10.9+), case-hardened, and spring steel.
- Prevention: Bake at 190-220C within 4 hrs of plating (ASTM F519 / ISO 4042).
- Preferred alternatives: Geomet 321, Mechanical Zinc, Zinc-Tin. Zero HE risk from process.
- Note: Zinc-Nickel has lower HE risk than plain zinc due to plating permeability, but is not zero.
- Thread tolerance: Thick coatings (HDG, heavy zinc) may require over-tapped nuts or special clearances.
- Coefficient of Friction (CoF): Dry zinc can have CoF 0.12-0.20. Wax or PLUS ML topcoats target 0.09-0.16.
- Galling risk (stainless): Use wax lube, nickel strike, electropolish, or Molykote for A2/A4 fasteners in stainless assemblies.
- Re-use: Geomet 321 with ML topcoat maintains CoF through multiple installation cycles. Plain zinc degrades.
- $ (Zinc Clear 3-5um): Interior, dry, non-critical. Short service life acceptable.
- $$ (Zinc Yellow with sealant, Mechanical Zinc): Outdoor, moderate exposure, 5-10 yr life.
- $$$ (Zinc Nickel, Geomet 321): Automotive, 10+ yr, or high-hardness requirements.
- $$$$ (Zinc Nickel 12ES, GEOBLACK): Premium aesthetics + extreme corrosion. Marine, luxury automotive, architecture.
| Finish | Corrosion Resist. | HE Risk | RoHS | Cost | Best For |
|---|---|---|---|---|---|
| Zinc Clear (Cr3 Trivalent) | Yes | Yes | $$ | Interior, general purpose | |
| Zinc Yellow (Cr3 Trivalent) | Yes | Yes | $$ | Outdoor, moderate exposure | |
| Black Zinc (Cr3 + Sealant) | Yes | Yes | $$ | Black aesthetic, moderate protection | |
| Zinc Nickel Clear (12B+S) | Low | Yes | $$$ | Automotive, high-cycle assemblies | |
| Black Zinc Nickel (12ES) | Low | Yes | $$$ | Premium black, 1000+ hr protection | |
| Geomet 321 + ML Clear | None | Yes | $$$$ | High-hardness, automotive critical | |
| Mechanical Zinc (Clear) | None | Yes | $$ | Washers, HE-sensitive parts | |
| Hot Dip Galvanized | None | Yes | $$ | Structural, outdoor, large fasteners | |
| Passivation (Stainless) | None | Yes | $ | Stainless steel standard treatment | |
| Cadmium | Yes | No | $$$$ | Military only. Avoid in commercial. |
| Application | Recommended Finish | Why |
|---|---|---|
| General hardware, Grade 5/8, indoor | Zinc Clear Cr3 (Fe/Zn 5AN) | Low cost, RoHS, adequate protection for environment |
| Outdoor structural, Grade 5/8 | Zinc Yellow Cr3 + Sealant (Fe/Zn 8CNS) | 96+ hr white rust, RoHS, visible yellow for inspection |
| Automotive body, Grade 10.9 | Geomet 321 + PLUS ML | No HE risk on high-hardness, 720 hr salt spray, controlled CoF |
| High-hardness tapping screw | Geomet 321 + PLUS ML | Prevents cold welding, no HE, consistent drive torque |
| Black premium aesthetic + protection | Black Zinc Nickel (Fe/Zn-Ni 8ES) | 840 hr salt spray, RoHS, premium black appearance |
| Stainless fastener, standard | Passivation (ASTM A967) | Restores oxide layer, removes free iron, standard requirement |
| Stainless in stainless assembly | Passivation + Wax Lube | Mitigates galling risk on stainless-to-stainless thread engagement |
| Washer (HE sensitive) | Mechanical Zinc (ISO 12683) | No HE from process, adequate protection, cost effective |
| Marine / salt water exposure | Stainless A4 + Passivation | Stainless provides inherent corrosion resistance without coating |
| Military / extreme environment | Consult SBS Engineering | Application-specific; cadmium, special organics, or specialty alloys |
Disclaimer: This finish guide is provided for reference purposes only. Salt spray hours and corrosion resistance values are typical and may vary based on part geometry, base material condition, bath chemistry, and environmental exposure. Always verify finish specifications with your supplier. Specialty Bolt and Screw, Inc. makes no warranty regarding the accuracy or completeness of this information for any specific application.
Finishes and Coatings
Finishes and coatings play a critical role in the performance, longevity, and environmental compliance of fasteners. At SBS, we offer a variety of advanced coatings specifically engineered to meet the technical demands of industries such as automotive, aerospace, and heavy machinery, while adhering to increasingly stringent environmental and safety regulations. One of the most widely used finishes is zinc plating, including variations like zinc-nickel and zinc-aluminum, which offer enhanced corrosion resistance, particularly in harsh environments. Zinc-nickel, in particular, provides superior protection against salt spray, making it ideal for marine and automotive applications.
For applications requiring compliance with modern environmental standards, SBS offers coatings such as Geomet. Inorganic, corrosion-resistant coatings are free of heavy metals like cadmium, making them not only environmentally friendly but also safer for workers during application and disposal. Additionally, SBS now provides the option for trivalent chrome finishes, an alternative to hexavalent chrome, which is regulated due to its toxicity. Trivalent chrome offers similar corrosion resistance while meeting new environmental mandates. Another advanced option is the organic-based E-Coat (Electrophoretic Deposition), which is environmentally friendly, offers superior chemical resistance, and provides an even coating thickness, ensuring consistent performance across complex geometries.
SBS also integrates passivation treatments for stainless steel fasteners, which enhances their corrosion resistance and meets ISO 9001 and IATF 16949 standards. These processes ensure that fasteners not only comply with rigorous safety and environmental regulations but also deliver optimal mechanical performance in challenging environments. For a comprehensive overview of common finish options, including applicable standards, compliance, and SST performance, please review the PDF below. With detailed product descriptions and specifications available in the SBS E-Catalog, our customers can confidently select the right coatings that ensure both regulatory compliance and superior performance for their specific needs.