Fastener Material & Finish Guide
Fastener Material & Finish Guide
Mutual Screw & Supply · mutualscrew.com · (800) 222-0324
Base material determines fundamental strength, corrosion behavior, weight, and cost. Coatings and finishes (see next tabs) can extend the life of carbon steel in corrosive environments, but for severe or permanent exposure, start with the right base material.
Low Carbon Steel
SAE 1006–1022 · Grade 2 / Class 4.6
Tensile strength
Corrosion resistance
Weldability
Cost
General purpose. Most economical option. Requires coating for any outdoor or moisture exposure. Common for anchors, wood screws, sheet metal screws, and light machine screws.
Medium Carbon Steel
SAE 1030–1045 · Grade 5 / Class 8.8
Tensile strength
Corrosion resistance
Weldability
Cost
Standard structural bolt material. Quenched and tempered for Grade 5 / 8.8 and above. Most automotive and machinery bolts. Requires coating outdoors.
Medium Carbon Alloy Steel
SAE 4037–4340 · Grade 8 / Class 10.9–12.9
Tensile strength
Corrosion resistance
Weldability
Cost
High-strength bolts. Chromium, molybdenum, or nickel additions increase hardenability. Suspension bolts, drivetrain hardware, heavy equipment. Not for galvanizing at Grade 8+.
18-8 Stainless Steel
AISI 304 · A2-70 · Most common SS
Tensile strength
Corrosion resistance
Weldability
Cost
Most common stainless grade. Excellent general corrosion resistance. Food service, outdoor hardware, pharmaceutical, light marine. Not for chloride-heavy environments.
316 Stainless Steel
AISI 316 · A4-70/80 · Marine grade
Tensile strength
Corrosion resistance
Weldability
Cost
Adds molybdenum for superior chloride resistance. Marine hardware, coastal construction, pool equipment, chemical processing. The correct choice where 304 would pit.
410 Stainless Steel
AISI 410 · Martensitic SS · Hardened
Tensile strength
Corrosion resistance
Weldability
Cost
Hardenable stainless. Stronger than 304/316 but less corrosion resistant. Self-drilling screws, concrete screws, wood screws. Not suitable for marine or chemical exposure.
Silicon Bronze
C65100 / C65500 · Non-ferrous
Tensile strength
Corrosion resistance
Weldability
Cost
Traditional marine fastener. No galvanic corrosion with copper alloy fittings. Boatbuilding, marine joinery, historic restoration. Expensive — use where 316 SS causes galvanic issues.
Brass
C36000 · Free-machining
Tensile strength
Corrosion resistance
Weldability
Cost
Decorative and electrical applications. Non-magnetic, non-sparking, good conductivity. Electrical panels, plumbing, decorative hardware. Not for structural or high-load use.
Nylon / Plastic
Nylon 6/6 · HDPE · PEEK
Tensile strength
Corrosion resistance
Weldability
Cost
Non-conductive, non-magnetic, chemically inert. Electronics, chemical processing, food service. Light loads only. PEEK for high-temp environments.
Stainless steel fasteners are not all alike. The grade determines corrosion resistance, strength, and magnetic properties. "Stainless" on a product label tells you almost nothing — always ask for the alloy designation.
| Grade | Series | Key Alloys | Magnetic? | Tensile (psi) | Corrosion Resistance | Best Application |
|---|---|---|---|---|---|---|
| Austenitic (Most Common) — Non-Hardenable, Generally Non-Magnetic | ||||||
| 304 / 18-8 | 300 | 18% Cr, 8% Ni | No (slight after cold work) | 70,000–100,000 | Excellent general; not chlorides | Food service, outdoor, pharmaceutical |
| 304L | 300 | 18% Cr, 8% Ni, low C | No | 70,000 | Same as 304 + better weld zones | Welded assemblies in 304 environments |
| 316 | 300 | 16% Cr, 10% Ni, 2% Mo | No | 70,000–100,000 | Superior; resists chlorides & acids | Marine, coastal, chemical, pool |
| 316L | 300 | 16% Cr, 10% Ni, 2% Mo, low C | No | 70,000 | Same as 316 + better weld zones | Welded marine or chemical assemblies |
| 321 | 300 | 18% Cr, 9% Ni, Ti stabilized | No | 75,000 | Good general; resists sensitization | High-temperature (up to 1,500°F) |
| Martensitic — Hardenable, Magnetic | ||||||
| 410 | 400 | 12% Cr | Yes | 70,000–190,000 | Moderate; not for wet/chemical | Self-drilling screws, concrete screws |
| 416 | 400 | 12–14% Cr, S or Se | Yes | 75,000–150,000 | Moderate; slightly less than 410 | Machined fasteners where 410 applies |
| 431 | 400 | 16% Cr, 2% Ni | Yes | 125,000–200,000 | Good; better than 410 | High-strength bolts in mild marine |
| Ferritic — Non-Hardenable, Magnetic | ||||||
| 430 | 400 | 17% Cr | Yes | 65,000 | Good atmospheric; not for acids | Decorative trim, appliances |
| Precipitation Hardening | ||||||
| 17-4 PH | 600 | 17% Cr, 4% Ni, Cu | Yes | 150,000–200,000 | Similar to 304 | Aerospace, high-strength stainless |
Galling warning: Austenitic stainless (304, 316) is prone to galling (thread seizing) when tightening stainless nuts on stainless bolts. Use an anti-seize lubricant — never torque dry. This is one of the most common stainless fastener installation errors.
Coating selection should match the environment and structural requirements. Some coatings add significant thickness and affect thread fit — always specify coated fasteners when critical tolerances are involved.
| Finish | Process | Thickness | Salt Spray (hrs) | Thread Impact? | Temp Limit | Best For |
|---|---|---|---|---|---|---|
| Zinc-Based Coatings | ||||||
| Zinc Plated (Clear) | Electroplating | 0.0002" | 12–36 | Minimal | 250°F | Indoor, light service, general hardware |
| Zinc Plated (Yellow) | Electroplating + chromate | 0.0002" | 96–200 | Minimal | 250°F | Grade 5 bolts, automotive, outdoor moderate |
| Hot-Dip Galvanized (HDG) | Molten zinc bath | 0.001"–0.004" | 1,000+ | Significant — use HDG nuts | 392°F | Structural outdoor, construction, anchors |
| Mechanical Galvanizing | Tumbling with zinc powder | 0.001"–0.002" | 500–1,000 | Moderate — use oversized nuts | 250°F | Alternative to HDG for high-strength bolts |
| Zinc Flake (Geomet®/Dacromet®) | Dip-spin coating | 0.0003"–0.0008" | 500–1,000 | Minimal | 500°F | Automotive, high-strength, no hydrogen risk |
| Other Metallic Coatings | ||||||
| Black Oxide | Chemical conversion | Negligible | 3–5 (dry) / 100+ (oiled) | None | 300°F | Appearance, mild corrosion delay, tooling |
| Nickel Plated | Electroplating | 0.0002"–0.0005" | 200–500 | Minimal | 1,200°F | Electronics, decorative, high-temp |
| Chrome Plated | Electroplating | 0.0002" | 200–300 | Minimal | 1,200°F | Decorative, automotive trim |
| Cadmium Plated | Electroplating | 0.0002" | 200–400 | Minimal | 450°F | Aerospace (restricted — toxic) |
| Non-Metallic Coatings | ||||||
| Phosphate + Oil | Chemical + lubricant | Negligible | 50–200 | None | 300°F | Lubrication, break-in, mild protection |
| PTFE / Teflon Coating | Spray/bake | 0.0005"–0.002" | 200–500 | Some — check fit | 500°F | Torque-tension control, food/chemical |
| Epoxy Powder Coat | Electrostatic spray + bake | 0.002"–0.004" | 500–1,000 | Significant — not for threaded shafts | 300°F | Structural heads, non-thread surfaces |
Hydrogen embrittlement warning: Electroplating processes (zinc, cadmium, chrome) can introduce hydrogen into high-strength steel (Grade 8, Class 10.9, 12.9), causing delayed brittle fracture. Parts must be baked within 4 hours of plating. For bolts above 150,000 psi tensile, mechanical galvanizing or zinc flake coatings are preferred over electroplating.
Corrosion resistance comparison — ratings reflect general performance. Actual service life depends on temperature, concentration, coating integrity, and galvanic coupling with adjacent materials. ✦ = Excellent · ✓ = Good · ~ = Marginal · ✗ = Not recommended.
| Material / Finish | Indoor Dry | Outdoor / Weathering | High Humidity | Salt Air / Coastal | Direct Marine | Chemical / Acid | Food / Sanitary | High Temp (500°F+) |
|---|---|---|---|---|---|---|---|---|
| Carbon Steel | ||||||||
| Plain carbon steel | ✦ | ✗ | ✗ | ✗ | ✗ | ✗ | ✗ | ~ |
| Zinc plated (clear) | ✦ | ~ | ~ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Zinc plated (yellow) | ✦ | ✓ | ✓ | ~ | ✗ | ✗ | ✗ | ✗ |
| Hot-dip galvanized | ✦ | ✦ | ✦ | ✓ | ~ | ✗ | ✗ | ✗ |
| Zinc flake (Dacromet) | ✦ | ✦ | ✦ | ✓ | ~ | ✗ | ✗ | ✓ |
| Black oxide (oiled) | ✦ | ✗ | ~ | ✗ | ✗ | ✗ | ✗ | ~ |
| Stainless Steel | ||||||||
| 410 SS | ✦ | ✓ | ✓ | ~ | ✗ | ✗ | ~ | ✓ |
| 304 / 18-8 SS | ✦ | ✦ | ✦ | ✓ | ~ | ~ | ✦ | ✓ |
| 316 SS | ✦ | ✦ | ✦ | ✦ | ✓ | ✓ | ✦ | ✓ |
| 17-4 PH SS | ✦ | ✦ | ✦ | ✓ | ~ | ~ | ✦ | ✓ |
| Non-Ferrous | ||||||||
| Silicon bronze | ✦ | ✦ | ✦ | ✦ | ✦ | ~ | ✓ | ✗ |
| Brass | ✦ | ✓ | ✓ | ~ | ~ | ~ | ✓ | ✗ |
| Nylon / plastic | ✦ | ✓ | ✦ | ✦ | ✦ | ✦ | ✦ | ✗ |
Galvanic corrosion: When two dissimilar metals contact each other in a conductive environment (moisture), the less noble metal corrodes faster. Common problem pairs: steel bolt in aluminum structure, stainless in carbon steel, brass in steel. Use isolation washers, compatible materials, or conductive grease to mitigate.
Quick selection guide — match your application environment to the correct material and finish combination. When in doubt, upgrade rather than downgrade — the cost difference is small compared to failure or premature replacement.
| Environment | First Choice | Second Choice | Avoid | Notes |
|---|---|---|---|---|
| Dry / Indoor | ||||
| Interior, climate controlled | Plain or zinc-plated carbon steel | Stainless (overkill) | — | Most economical choice; no corrosion risk |
| Interior, high humidity (greenhouse, laundry) | Zinc yellow / HDG | 304 SS | Plain steel | Condensation causes rust on plain steel quickly |
| Food processing / sanitary | 316 SS (electropolished) | 304 SS | Any plated carbon steel | Plating can contaminate; 316 required for USDA/FDA |
| Outdoor / Exposed | ||||
| General outdoor (non-coastal) | Hot-dip galvanized | 304 SS or zinc flake | Zinc electroplated | HDG provides 20–50 year life in typical outdoor service |
| Pressure-treated lumber (ACQ/CA) | Hot-dip galvanized (ASTM A153) or 316 SS | 316 SS | Zinc plated, plain, 304 SS | ACQ/CA treatments are corrosive to zinc and 304 SS |
| Coastal / salt air (within 1 mile of ocean) | 316 SS | HDG with frequent inspection | 304 SS, zinc plated | 316 is the minimum for coastal; silicon bronze for submerged |
| Direct marine (submerged or splash zone) | 316 SS or silicon bronze | Titanium (specialty) | 304 SS, any carbon steel | 316 still pits in prolonged submersion; silicon bronze is traditional standard |
| Industrial / Specialty | ||||
| Chemical / acid exposure | 316 SS or Hastelloy | Nylon/PTFE (light loads) | Carbon steel, 304 SS, brass | Check specific chemical compatibility — no single answer |
| High temperature (300–800°F) | Alloy steel (A286) or 321 SS | 316 SS to 500°F | Zinc or cadmium coatings | Most zinc coatings volatilize above 400°F |
| High temperature (800–1800°F) | Inconel / Hastelloy | 310 SS | Standard carbon or SS | Specialty alloys only; standard stainless loses strength rapidly above 800°F |
| Cryogenic / very low temp | 316L SS or A286 | Inconel | High-carbon steel | Carbon steel becomes brittle below −40°F; austenitic SS retains toughness |
| Automotive / high-vibration | Grade 8 / Class 10.9 with zinc flake | Grade 8 yellow zinc | Plain carbon steel | Zinc flake preferred — no hydrogen embrittlement risk at high strength levels |
| Electrical / electronics | Brass or stainless | Nickel plated carbon | Zinc plated (contact resistance) | Brass for conductivity; stainless for non-magnetic; nylon for isolation |
| Pool / chlorinated water | 316 SS | Silicon bronze | 304 SS, HDG, any carbon steel | Chlorine attacks 304 SS; 316 is minimum standard for pool hardware |
Shop by Material & Finish at Mutual Screw & Supply
We stock fasteners in plain, zinc, hot-dip galvanized, 18-8 stainless, 316 stainless, and specialty materials — from standard hardware to military and aerospace specifications. Family owned since 1947.
© 2026 Mutual Screw & Supply · 68 West Passaic Street, Rochelle Park, NJ 07662 · mutualscrew.com
Material properties per ASTM, SAE, and ISO standards. Corrosion ratings are general guidance — actual performance varies with temperature, concentration, surface condition, and application. Consult material certifications and an engineer for critical applications.