Fastener Material & Finish Guide
How to choose the right fastener material and finish. Compare carbon steel, stainless grades, bronze, brass and nylon, see how zinc, galvanized and other coatings hold up, and find the best fastener for every environment.
Base MaterialsStainless GradesCoatings & FinishesCorrosion RatingsBy EnvironmentFAQ
Fastener Base Materials Compared
Base material determines fundamental strength, corrosion behavior, weight and cost. Coatings and finishes can extend the life of carbon steel in corrosive environments, but for severe or permanent exposure, start with the right base material. Ratings are relative on a 1 to 5 scale. For cost, more dots means more expensive.
Low Carbon Steel
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.
Shop Grade 2 hex cap screws →Medium Carbon Steel
Standard structural bolt material. Quenched and tempered for Grade 5 / 8.8 and above. Most automotive and machinery bolts. Requires coating outdoors.
Shop Grade 5 hex cap screws →Medium Carbon Alloy Steel
High-strength bolts. Chromium, molybdenum, or nickel additions increase hardenability. Suspension bolts, drivetrain hardware, heavy equipment. Not for galvanizing at Grade 8+.
Shop Grade 8 hex cap screws →18-8 Stainless Steel
Most common stainless grade. Excellent general corrosion resistance. Food service, outdoor hardware, pharmaceutical, light marine. Not for chloride-heavy environments.
Shop 18-8 stainless machine screws →316 Stainless Steel
Adds molybdenum for superior chloride resistance. Marine hardware, coastal construction, pool equipment, chemical processing. The correct choice where 304 would pit.
Shop 316 stainless machine screws →410 Stainless Steel
Hardenable stainless. Stronger than 304/316 but less corrosion resistant. Self-drilling screws, concrete screws, wood screws. Not suitable for marine or chemical exposure.
Shop 410 stainless machine screws →Silicon Bronze
Traditional marine fastener. No galvanic corrosion with copper alloy fittings. Boatbuilding, marine joinery, historic restoration. Expensive. Use where 316 SS causes galvanic issues.
Shop silicon bronze machine screws →Brass
Decorative and electrical applications. Non-magnetic, non-sparking, good conductivity. Electrical panels, plumbing, decorative hardware. Not for structural or high-load use.
Shop brass machine screws →Nylon / Plastic
Non-conductive, non-magnetic, chemically inert. Electronics, chemical processing, food service. Light loads only. PEEK for high-temp environments.
Shop nylon machine screws →Stainless Steel Grades: 304 vs 316, 410 and More
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, so 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 |
Fastener Coatings & Finishes: Zinc, Galvanized, Black Oxide and More
Coating selection should match the environment and structural requirements. Some coatings add significant thickness and affect thread fit, so 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 |
Corrosion Resistance by Material and Environment
Ratings reflect general performance. Actual service life depends on temperature, concentration, coating integrity and galvanic coupling with adjacent materials.
| 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 | Excellent | Avoid | Avoid | Avoid | Avoid | Avoid | Avoid | Marginal |
| Zinc plated (clear) | Excellent | Marginal | Marginal | Avoid | Avoid | Avoid | Avoid | Avoid |
| Zinc plated (yellow) | Excellent | Good | Good | Marginal | Avoid | Avoid | Avoid | Avoid |
| Hot-dip galvanized | Excellent | Excellent | Excellent | Good | Marginal | Avoid | Avoid | Avoid |
| Zinc flake (Dacromet) | Excellent | Excellent | Excellent | Good | Marginal | Avoid | Avoid | Good |
| Black oxide (oiled) | Excellent | Avoid | Marginal | Avoid | Avoid | Avoid | Avoid | Marginal |
| Stainless steel | ||||||||
| 410 SS | Excellent | Good | Good | Marginal | Avoid | Avoid | Marginal | Good |
| 304 / 18-8 SS | Excellent | Excellent | Excellent | Good | Marginal | Marginal | Excellent | Good |
| 316 SS | Excellent | Excellent | Excellent | Excellent | Good | Good | Excellent | Good |
| 17-4 PH SS | Excellent | Excellent | Excellent | Good | Marginal | Marginal | Excellent | Good |
| Non-ferrous | ||||||||
| Silicon bronze | Excellent | Excellent | Excellent | Excellent | Excellent | Marginal | Good | Avoid |
| Brass | Excellent | Good | Good | Marginal | Marginal | Marginal | Good | Avoid |
| Nylon / plastic | Excellent | Good | Excellent | Excellent | Excellent | Excellent | Excellent | Avoid |
Best Fastener Material for Every Environment
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) | None | 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 |
Frequently Asked Questions
What is the difference between 304 and 316 stainless steel fasteners?
316 adds about 2% molybdenum, which gives it superior resistance to chlorides and acids. Use 316 for marine, coastal, pool and chemical applications. 304 (18-8) is the most common stainless grade and works well for food service, outdoor hardware and light marine use, but it can pit in chloride-heavy environments.
Is hot-dip galvanized better than zinc plated?
For outdoor use, yes. Hot-dip galvanizing is 0.001" to 0.004" thick and rated 1,000+ hours in salt spray, compared with 12 to 36 hours for clear zinc plating. The thicker coating affects thread fit, so pair HDG bolts with HDG nuts. Zinc plating is the economical choice for indoor and light service.
What fasteners should I use with pressure-treated lumber?
Use hot-dip galvanized (ASTM A153) or 316 stainless. ACQ and CA lumber treatments are corrosive to zinc plated, plain steel and 304 stainless fasteners.
Are stainless steel fasteners magnetic?
300 series austenitic grades such as 304 and 316 are generally non-magnetic, though 304 can become slightly magnetic after cold work. 400 series grades (410, 416, 431, 430) and 17-4 PH are magnetic.
How do I prevent galling on stainless steel bolts?
Austenitic stainless (304, 316) is prone to galling, or thread seizing, when stainless nuts are tightened on stainless bolts. Use an anti-seize lubricant and never torque dry.
What is hydrogen embrittlement?
Electroplating (zinc, cadmium, chrome) can introduce hydrogen into high-strength steel such as Grade 8, Class 10.9 and 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.
What is galvanic corrosion and how do I prevent it?
When two dissimilar metals touch in the presence of moisture, the less noble metal corrodes faster. Common problem pairs are a steel bolt in aluminum, stainless in carbon steel, and brass in steel. Use isolation washers, compatible materials or conductive grease.
Need help choosing a material?
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. Serving customers since 1947.
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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.