Fastener materials are the base metals and polymers used to make bolts, screws, nuts, and other threaded hardware, from carbon steel and stainless to aluminum, titanium, and engineered plastics. Three factors drive every selection: the mechanical strength the joint must carry, the corrosion resistance the environment demands, and the cost the project can bear. This guide compares common fastener materials, their strength grades, and the coating families that protect them, then maps each option to real service environments.
The Three Decisions Behind Every Fastener Spec
Every fastener specification breaks down into three independent decisions. Get any one wrong and the joint either costs too much or fails early in service. The first decision is the material, meaning the base metal or polymer. The material sets the corrosion behavior, the density, and much of the unit price. Carbon steel is cheap and strong but rusts without protection. Stainless resists corrosion by forming a passive film. Aluminum saves weight. Titanium and engineered plastics cover extreme or specialist duty.
The second decision is the strength grade. Within a given material, heat treatment and composition set how much load the part carries. A grade is a property class such as ISO 8.8 for carbon steel or A2-70 for stainless. The grade tells the buyer the minimum tensile and yield strength, not the alloy family. Two bolts in different materials can share the same grade yet behave very differently in the field, because the material still governs corrosion and temperature limits.
The third decision is the coating or surface treatment. The coating protects the base material from the environment and can change how the thread fits. Zinc plating, hot dip galvanizing, anodizing, and other finishes each trade thickness, cost, and salt spray life. Choose the coating after the material and grade are fixed, because the coating cannot add strength the part does not already have.
Treat the three as a sequence. Pick the material for the environment, set the grade for the load, then coat for extra life. Specifiers who reverse the order, choosing a material for its strength alone and ignoring corrosion, are the ones who see rusted failures a few months after installation. The rest of this guide fills in each decision with numbers you can use on a drawing.
A useful habit is to write the three decisions on the drawing as three separate lines: material, grade, and coating. When a failure occurs, you can then trace which line was wrong instead of guessing at the cause. Many plants keep a one page selector that lists the environment on the left and the material, grade, and coating triple on the right, which removes the most common ambiguity at the purchasing desk and keeps the conversation in one consistent language.
Fastener Material Families Compared
Strength and corrosion rarely peak in the same alloy, which is the central tension of fastener selection. A very strong carbon steel rusts fastest, while the most corrosion resistant stainless is modest in strength until you pay for cold worked or special classes. The table keeps the comparison honest by showing both numbers next to the price, so you can see the trade before you specify rather than after a joint has failed in the field.
| Material | Typical tensile strength (MPa) | Korrosionsbeständigkeit | Maximale Betriebstemperatur (°C) | Relative cost index | Am besten geeignet für |
|---|---|---|---|---|---|
| Carbon steel (Grade 8.8) | 800+ (indicative) | Poor, needs coating | ~300 | 1.0 | Allgemeine Zwecke |
| Alloy steel (10.9/12.9) | 1000–1200 | Schlecht | ~300 | 1.3 | High strength structural |
| Stainless 304 / A2-70 | 700 | Good (PREN ~19) | 425 cont. / 870 int. | 3.0 | Indoor / wet |
| Stainless 316 / A4-70 | 700 | Excellent (PREN ~24–26) | 425 cont. / 870 int. | 4.0 | Coastal / chemical |
| Aluminum (6061-T6) | 310 | Good (oxide film) | ~150 | 2.5 | Light weight |
| Messing | 300–500 | Good, not chloride | ~200 | 3.0 | Decorative / low load |
| Titanium (Grade 5) | 1100 | Excellent (seawater) | ~400 | 10+ | Aerospace / marine |
| Nylon / PEEK | 50–90 | Hervorragend | 80–250 | high | Electrical / chemical |
Values indicative / approximate, confirm against the governing standard.
Carbon steel fasteners are the workhorse of the industry because they deliver the best strength for the money. A Grade 8.8 carbon bolt reaches about 800 MPa tensile, enough for most structural and machine joints, while plain low carbon grades serve non critical indoor hardware. The weakness is corrosion: bare carbon steel rusts as soon as it sees moisture, so nearly every outdoor or humid application depends on a coating to survive. That coating is a separate decision, covered later, and it adds cost and thickness the base material does not. For buyers watching budget, carbon steel is usually the right start, then you spend on the surface treatment the environment forces. Our Befestigungselemente aus Kohlenstoffstahl
Legierungsstahl BefestigungselementeZ guide covers the details.
Stainless resists corrosion by forming a thin, self healing chromium rich passive film, so they need no coating in many indoor and wet environments. The two common families are 304, called A2, for general indoor and architectural use, and 316, called A4, which adds molybdenum for resistance to chlorides and chemical attack. Both sit near 700 MPa tensile in the popular A2-70 and A4-70 classes, with PREN values around 19 for 304 and 24 to 26 for 316, a useful proxy for pitting resistance that moves with molybdenum content. Stainless costs more than carbon steel and work hardens when machined, but it removes the coating step in mild service. Our Edelstahl Befestigungselement Klassen
Aluminium-Befestigungselemente guide for selection detail.
Brass serves decorative, low load, and electrical roles. It resists corrosion in most atmospheres but not in chloride or marine settings, and it is softer than steel, so it will not carry structural load. Brass is easy to machine and looks good in visible hardware, that is why it appears in fixtures, instruments, and terminals.
Titanium delivers excellent strength to weight and outstanding seawater corrosion resistance, which earns them a place in aerospace and marine service where steel would rust or aluminum would be too weak. The cost is high, often an order of magnitude above steel, so titanium is reserved for joints where its properties pay for themselves, such as subsea or flight critical hardware.
Engineered plastics such as nylon and PEEK make parts that are non conductive, non magnetic, and chemically inert. They suit electrical, food, and corrosive chemical duty where metal would corrode or short a circuit, but their strength is a fraction of metal, roughly 50–90 MPa. Our Nylon und PEEK Befestigungselemente guide explains where they fit, and our metal density table
Strength Grades in One Table
| System | Class/Grade | Mindestzugfestigkeit Rm (MPa) | Min yield ReL (MPa) | Härte |
|---|---|---|---|---|
| ISO 4.6 | 4.6 | 400 | 240 | 116–220 HV |
| ISO 8.8 | 8.8 | 800 | 640 | 250–320 HV (22–32 HRC) |
| ISO 10.9 | 10.9 | 1000 | 900 | 320–380 HV (32–39 HRC) |
| ISO 12.9 | 12.9 | 1200 | 1080 | 380–435 HV (39–44 HRC) |
| SAE Grade 2 | 2 | 413 | varies | varies |
| SAE Grade 5 | 5 | 827 | 689 | 25–34 HRC |
| SAE Grade 8 | 8 | 1138 (165 ksi) | 1034 | 33–39 HRC |
| ISO A2-70 | A2-70 | 700 | 450 | 210 HV min |
| ISO A4-70 | A4-70 | 700 | 450 | 210 HV min |
Values indicative / approximate; consult the governing standard for proof load and exact limits.
Read the grade before you trust the bolt. Most carbon and alloy steel hex heads are marked with the class on the top, and stainless is marked A2 or A4 with the strength number, so the part identifies itself on the bench. A higher grade is not automatically better: it costs more, is harder, and on very high strength steel it demands hydrogen relief baking after plating. Match the grade to the actual clamp load and the safety factor in the design, not to a habit of always buying the strongest available. The values above are indicative and vary by product standard, so confirm against the source document when the joint is safety related. This page gives the quick comparison only and does not reproduce the full grade or marking tables, those live on the dedicated charts linked below.
When a drawing only shows 8.8 with no material named, assume carbon or alloy steel, because stainless uses the A2 or A4 letter code instead. Mixing the two systems is a frequent source of error on cross border jobs, where an inch drawing may call Grade 5 and a metric drawing calls 8.8 for what is nearly the same strength. Confirm the system before you substitute, because the thread form and head dimensions differ even when the strength lines up, and a wrong assumption there can fail the assembly.
For the complete grade listing with proof loads and head markings, see our Schraubenfestigkeitsklasse-Karte, and for identifying marks on hex heads, see our grade marking chart
Matching Material to Environment
ASTM B117) as a credibility anchor. Salt spray hours are a comparative lab measure, not a field life guarantee, but they show the order of magnitude between a zinc plated indoor screw and a 316 marine bolt.
| Umwelt | Empfohlen Werkstoff | Recommended coating | Indicative ASTM B117 salt spray (h) |
|---|---|---|---|
| Indoor dry | Kohlenstoffstahl | None or black oxide | Minimal |
| Outdoor, rain | Carbon steel + zinc plating | Chromate (see note) | 96–240 (with chromate) |
| Coastal / marine | 316 (A4) | None or anodized (Al) | 1000+ (316) |
| Chemical / industrial | 316 (A4) or PEEK | As applicable | Hoch |
| High temp | Alloy or stainless | Keine | Per temp limit |
Indicative ASTM B117 salt spray hours, approximate and environment dependent.
For sheltered outdoor use, carbon steel with a zinc coating performs well and stays economical, so it dominates fences, enclosures, and light structural steel. Near the coast, or in constant humidity and de icing salt, the chloride load defeats plain zinc, and the right move is 316 stainless steel (A4). The PREN value near 24 to 26 for 316, against about 19 for 304, is the reason: the higher pitting resistance equivalent number means 316 resists chloride attack far better. Aluminum with anodizing works where weight matters and the load is light. Always pair the material with the right coating and avoid coupling dissimilar metals that invite galvanic corrosion, covered later in this guide.
Why does stainless still rust if it is the corrosion answer? The passive film can break down under deposits, low oxygen, or chlorides, and once it pits, the damage is local and fast. The mechanism is explained in our why stainless steel still rusts guide, and the coastal choice between the two grades is detailed in our 304 vs 316 stainless steel comparison. This guide does not re open that debate, it points you to the dedicated pages so the data stays where buyers expect it.
Coatings and Surface Treatments: The Full Menu
| Beschichtung | Prozess | Typical thickness (µm) | Salt spray (B117, h) | Relative cost | Anmerkung |
|---|---|---|---|---|---|
| Zinc electroplating (B633) | Electrolytic | 5–25 | 96–240 (chromated) | 1.0 | Thin, economical |
| Hot dip galvanizing (A153) | Molten dip | 45–85 (bolt) | 500–1500 | 1.5 | Thick, outdoor |
| Mechanical galvanizing | Cold peen | 25–150 | Gut | 1.5 | No H embrittlement |
| Zinc flake (Geomet) | Dip spin | 8–25 | 480–1000 | 2.0 | No H embrittlement |
| Black oxide | Chemical | <1 | Minimal | 0.8 | Cosmetic |
| Nickel / chrome | Electrolytic | 10–50 | Gut | 3.0 | Decorative |
| PTFE / Xylan | Dip | 10–25 | Excellent release | 3.0 | Low friction |
| Anodizing (Al) | Electrolytic | 5–25 | Gut | 1.5 | Hardens surface |
| Passivation (SS) | Chemical | nm | Enhances | 0.5 | Corrosion boost |
| Phosphate | Chemical | 1–10 | Base for paint | 1.0 | Primer |
Values indicative / approximate; salt spray depends on thickness and sealer.
Zinc electroplating is the thin, economical default for indoor and light outdoor hardware, and it keeps thread tolerances tight because the film is only 5 to 25 microns. A zinc bolt therefore suits high volume assemblies where cost and fit matter more than outdoor life. Hot dip galvanizing is the thick, long life option for structural steel exposed to weather, at the price of swollen threads. Zinc flake coatings such as Geomet give high salt spray resistance with no hydrogen embrittlement risk, which means they appear on automotive and high strength parts. Black oxide is cosmetic with minimal protection, nickel and chrome are decorative and corrosion resistant, and PTFE topcoats cut friction. Aluminum uses anodizing, and stainless uses passivation to rebuild its film.
The electroplating principle behind zinc and many other finishes is laid out on the Electroplating page at Wikipedia, and the base metal behavior is covered at the Zinc und Edelstahl references, with passivation detail at the Passivation chemistry page. For the deep dive on the most specified finish, see our Verzinkung guide. To choose between the two zinc families, our galvanized vs zinc plated comparison weighs thickness, cost, and thread fit, and our anodizing for fasteners guide covers the aluminum process end to end.
Coating Thickness vs Thread Fit
For tight fit classes, the fix is decided before plating: increase the tap size on the nut so the coated thread still clears, or cut the threads after coating so the plating sits on the finished form. Agree the plating thickness with the supplier up front, because the effect grows as diameter shrinks. A coarse thread in M20 shrugs off a few microns, but a fine M3 thread can seize once coated. Threads that look fine unmated can lock up after plating, so thread fit must be specified together with the coating, not added as an afterthought on the purchase order.
Hydrogen embrittlement is the other coating risk on strong steel. Acid pickling and plating can introduce hydrogen, and on hard, high strength parts that hydrogen can drive sudden brittle failure months later. ASTM B633 requires hydrogen relief baking on high strength steel, with the bake applied above roughly 1000 MPa tensile, and the standard notes a practical ceiling near 1700 MPa (247 ksi, 46 HRC) above which electroplated zinc is normally avoided. If your fastener sits in that range, switch to a coating with no acid step, such as mechanical galvanizing or zinc flake, rather than betting on the bake. The coating also changes the friction under the head, and that changes the torque to preload relationship, so our coefficient of friction guide and Drehmoment Zugfestigkeit chart show how plating moves the numbers, with our tensile strength converter for any unit switch. The electroplating route and its hydrogen risk are covered in our zinc plating guide.
Galvanic Corrosion: The Assembly Killer
| Metall | Potential vs SHE (V) |
|---|---|
| Gold | +1.50 |
| Platinum | +1.20 |
| Titan | +0.10 |
| 316 SS (passive) | +0.10 |
| 304 SS (passive) | +0.00 |
| Carbon steel / iron | −0.50 |
| Aluminium | −0.80 |
| Zinc | −1.05 |
| Magnesium | −1.60 |
Seawater, indicative values, varies with condition.
The practical lesson is to keep partners close on the series. Aluminum against 316 stainless, at about 0.90 V apart, is a risky pairing in a wet joint, while titanium and 316 sit together and are safe. You avoid galvanic attack three ways: isolate the metals with a non conductive washer or a coating barrier, select partners near each other on the series, or make the smaller part the sacrificial one so it corrodes first and is cheap to replace. A zinc plated steel washer under a stainless bolt is a deliberate sacrifice, the zinc goes before the steel or the stainless. Coatings themselves act as the barrier, so plating choice matters as much as the base metal. The mechanism is detailed on the Galvanic corrosion page at Wikipedia. For the isolation hardware, size the right non conductive or coated washer from a washer dimensions chart, with the common standards listed in our dedicated guide.
Cost vs Performance: Where to Spend, Where to Save
| Material | Unit cost index | TCO note |
|---|---|---|
| Kohlenstoffstahl | 1.0 (add coating cost) | Coating extends life, plan for it |
| Stainless 304 | 3.0 | No coating needed in many uses |
| Stainless 316 | 4.0 | Best for coastal, fewer replacements |
| Aluminium | 2.5 | Saves handling weight |
| Titan | 10+ | Reserved for critical service |
| Nylon / PEEK | Hoch | Weight and corrosion savings offset price |
Unit cost index indicative / approximate.
Spend where the environment forces you to, and save where it does not. For dry indoor duty, carbon steel with a light zinc coating is the right economy call, and paying for stainless there is wasted money. For coastal or chemical service, the stainless premium buys years of life and avoids the labor of replacing a failed carbon bolt, so the total cost of ownership often favors the dearer material. Coatings extend the life of cheap steel, but a coating that fails in the wrong environment costs more than specifying the better base metal once. The weight side of cost matters too: our fastener weight calculator turns material and quantity into shipping and handling cost, which is where aluminum and plastics quietly pay back.
Standards You'll Be Asked to Name
The standards themselves are maintained by the bodies above, and the safest links are to the organizations rather than to deep pages that move or expire. For ASTM, start at ASTM International; for ISO at ISO; for SAE at SAE International; and for corrosion and coating science at AMPP, the body formed from NACE. ASTM B633-23, the current zinc electroplating revision, is one verified deep link worth keeping at ASTM B633-23. For how the DIN, ISO, ANSI, and ASME systems relate and which to cite on a global project, see our Befestigungselement Standards erklärt guide. This guide does not restate every standard, it points to the source and to the dedicated pages.
Seven Specification Mistakes to Avoid
Choosing by material alone and forgetting the grade. The alloy sets corrosion, the grade sets load, and you need both numbers on the spec.
Ignoring the environment. A strong carbon bolt in a coastal plant is a rusted bolt in a season, no matter the grade.
Letting the coating eat the thread. A thick plating on a tight class binds the nut, so spec the coated condition up front.
Coupling dissimilar metals without isolation. Aluminum against stainless in a wet joint is a galvanic failure waiting to happen.
Zinc plating very high strength steel. Above the embrittlement threshold, electroplated zinc needs a relief bake or a different coating entirely.
Buying on unit price only. The cheap bolt that fails costs more in downtime than the dearer material specified once.
Pairing a coating with an incompatible base. Some finishes do nothing for the substrate they sit on, so match the coating to the material, not to habit.
Each of these is covered earlier with its data, and the isolation fix for mistake four starts with the right washer, sized from our washer size chart. When the spec is set and you want a second opinion from a manufacturer, our ingenieurteam reviews material and grade choices against the environment.
Häufig gestellte Fragen
A: Ein Befestigungsmaterial ist das Grundmetall oder Polymer, aus dem das Teil besteht, wie Kohlenstoffstahl, Edelstahl, Aluminium oder Nylon. Ein Grad beschreibt das Festigkeitsniveau, das durch Wärmebehandlung und Zusammensetzung in diesem Material erreicht wird, am häufigsten ausgedrückt als ISO-Eigenschaftsklasse wie 8.8 oder A2-70. Sie wählen das Material zuerst für Korrosionsbeständigkeit und Kosten, dann die Qualität für die Last, die es tragen muss. Die beiden Entscheidungen sind unabhängig: Ein Edelstahlbolzen und ein Kohlenstoffstahlbolzen können die gleiche Stärke der Klasse 8,8 haben, verhalten sich aber in einer Meeresumwelt sehr unterschiedlich.
Wie wähle ich das richtige Befestigungsmaterial für den Außen- oder Küstenbereich?
A: Für den geschützten Außenbereich leistet Kohlenstoffstahl mit einer Zinkbeschichtung eine gute Leistung und bleibt wirtschaftlich. In Küstennähe oder bei konstanter Luftfeuchtigkeit wenden Sie sich an 316 Edelstahl (A4), der eine Lochfraßwiderstandsäquivalentzahl (PREN) von 24 bis 26 aufweist und einem Chloridangriff weit besser als 304 standhält. Aluminium mit anodisierenden Arbeiten, wo Gewicht zählt. Verbinden Sie das Material immer mit der richtigen Beschichtung und vermeiden Sie die Kopplung verschiedener Metalle, die galvanische Korrosion einladen. Wenn Sie Zweifel an strukturellen Küstenarbeiten haben, geben Sie A4 an und bestätigen Sie dies mit dem Projektstandard.
What are the most common fastener coating types?
A: The common options are zinc electroplating (thin, economical, good for indoor and light outdoor), hot dip galvanizing (thick, long life outdoors), zinc flake coatings such as Geomet (high salt spray resistance, no hydrogen risk), black oxide (cosmetic, minimal protection), nickel or chrome (decorative and corrosion resistant), and PTFE based topcoats for low friction. Aluminum parts use anodizing, and stainless parts use passivation. Each coating trades thickness, cost, and salt spray life differently, so match the coating to the environment rather than to habit.
Does coating thickness affect thread fit?
A: Yes, and this is where specifiers get surprised. A plating of 8 to 25 microns on a 6g or 6H thread can consume a large share of the tolerance, causing nuts to bind or gauges to fail. For tight fit classes, increase the tap size before plating or cut threads after coating, and agree the plating thickness with the supplier up front. The effect grows with smaller diameters. Threads that look fine unmated can seize once coated, so thread fit must be specified together with the coating, not after it.
What is galvanic corrosion and how do I avoid it in fasteners?
A: Galvanic corrosion happens when two dissimilar metals touch in the presence of an electrolyte, and the more active one corrodes faster. In fasteners, a carbon steel or aluminum part coupled to stainless steel is the classic failure. Avoid it by isolating the metals with a non conductive washer or coating, selecting partners close on the galvanic series, or making the smaller part the sacrificial one (for example a zinc plated washer). Coatings themselves act as the barrier, which is why plating choice matters as much as base material.
Which fastener material is best for high temperature service?
A: Carbon and alloy steels serve well up to roughly 300 C if not over stressed, while stainless grades such as 304 and 316 remain useful to about 425 C continuous and 870 C intermittent, limited by sensitization and strength loss. Titanium grades extend further and resist scaling, though cost rises sharply. Above these ranges, specify specialty alloys per the project standard. Always check both the temperature and the load, because a material that survives the heat may lose too much strength to hold the joint.
How much more do stainless steel fasteners cost than carbon steel?
A:
Literaturverzeichnis
. The standards body behind A307, A325, A490, F3125, A193, F593, F594, B633, B117, and F1941 cited in this guide.
. The verified current revision defining zinc electroplating thickness classes and hydrogen relief baking for high strength steel.
. The international body for ISO 898-1, ISO 3506, ISO 4042, and ISO 10683 referenced throughout.
. Source of SAE J429 inch series grade equivalents for carbon and alloy steel fasteners.
. Authority on corrosion science and coating practice referenced for galvanic and salt spray behavior.
. Background on the galvanic series and dissimilar metal attack used in the corrosion section.
. Reference for the passive film that makes stainless and the passivation process.
. Background on the electrolytic coating principle behind zinc and other platings.
. Reference for zinc as the metal behind galvanizing and its protective role over steel.
