This reference guide covers the most commonly used stainless steel grades in industrial fastener applications. Whether you are specifying fasteners for a new project, verifying material compatibility, or structuring your product catalog data, this guide provides the technical details you need.
### Stainless steel grades used in fasteners
The most common stainless steel grades for fastener manufacturing are 304 (A2), 316 (A4), 410, and 17-4 PH. Each grade has different properties that make it suitable for specific applications.
**304 Stainless Steel (A2)**
304 is the most widely used stainless steel grade for fasteners. It is the standard choice for general-purpose applications where corrosion resistance is needed but extreme environments are not a concern.
Composition: 18% chromium, 8% nickel, 0.08% max carbon, balance iron. This is why it is sometimes called 18-8 stainless.
Mechanical properties: Tensile strength 515 MPa (75 ksi) minimum. Yield strength 205 MPa (30 ksi) minimum. Elongation 40% minimum. Hardness up to Rockwell B92.
Fastener grades: A2-50 (500 MPa tensile, 210 MPa yield), A2-70 (700 MPa tensile, 450 MPa yield), A2-80 (800 MPa tensile, 600 MPa yield). A2-70 is the most commonly specified.
Applicable standards: ASTM A193/A193M, ASTM F593, DIN 934, DIN 933, ISO 3506.
Best for: General industrial applications, food processing equipment, architectural hardware, marine hardware in mild environments, chemical processing where chloride exposure is limited.
Not recommended for: Saltwater immersion, chloride-rich environments, high-temperature applications above 800F (425C), applications requiring magnetic permeability.
**316 Stainless Steel (A4)**
316 adds molybdenum to the 304 composition, significantly improving resistance to chloride corrosion and pitting. It is the standard choice for marine, chemical, and pharmaceutical applications.
Composition: 16% chromium, 10% nickel, 2% molybdenum, 0.08% max carbon, balance iron.
Mechanical properties: Tensile strength 515 MPa (75 ksi) minimum. Yield strength 205 MPa (30 ksi) minimum. Elongation 40% minimum. Hardness up to Rockwell B95.
Fastener grades: A4-50 (500 MPa tensile, 210 MPa yield), A4-70 (700 MPa tensile, 450 MPa yield), A4-80 (800 MPa tensile, 600 MPa yield).
Applicable standards: ASTM A193/A193M, ASTM F593, DIN 934, DIN 933, ISO 3506.
Best for: Marine and offshore applications, chemical processing, pharmaceutical equipment, coastal construction, swimming pool hardware, food processing with salt or acidic materials.
Price comparison: 316 fasteners typically cost 20-30% more than equivalent 304 fasteners.
**410 Stainless Steel**
410 is a martensitic stainless steel that can be heat-treated to achieve higher strength than 304 or 316. It offers moderate corrosion resistance with significantly higher hardness and strength.
Composition: 12% chromium, 0.15% max carbon, balance iron. No nickel.
Mechanical properties (heat-treated): Tensile strength 690-1100 MPa depending on heat treatment. Yield strength 415-860 MPa. Hardness up to Rockwell C40.
Applicable standards: ASTM A193 Grade B6, ASTM F593 Condition H.
Best for: Applications requiring high strength with moderate corrosion resistance. Valve components, pump shafts, turbine parts, bolting for high-temperature service.
Limitations: Significantly less corrosion-resistant than 304 or 316. Not suitable for marine or chemical environments.
**17-4 PH Stainless Steel**
17-4 PH (precipitation hardening) is a high-strength stainless steel used in demanding applications where both strength and corrosion resistance are required.
Composition: 17% chromium, 4% nickel, 4% copper, 0.3% niobium, balance iron.
Mechanical properties (Condition H900): Tensile strength 1310 MPa (190 ksi). Yield strength 1170 MPa (170 ksi). Hardness Rockwell C40-44.
Best for: Aerospace fasteners, nuclear applications, high-performance industrial equipment, applications requiring both high strength and corrosion resistance.
Price comparison: 17-4 PH fasteners cost significantly more than 304 or 316, typically 3-5 times the price of equivalent A2-70 fasteners.
### Common fastener dimensions and specifications
**Metric hex head bolts (DIN 933 / ISO 4017)**
Sizes range from M3 to M64. The most commonly stocked sizes in industrial supply are M6, M8, M10, M12, M16, and M20.
For M10 x 40mm hex bolt: Head height 6.63mm, width across flats 16mm, width across corners 18.48mm, thread pitch 1.5mm (coarse) or 1.25mm (fine).
Thread standards: ISO 261 (metric coarse), ISO 261 (metric fine). Coarse thread is standard unless fine thread is specified.
**Metric socket head cap screws (DIN 912 / ISO 4762)**
Head diameter is approximately 1.5 times the nominal diameter. Socket size is approximately 0.6 times the nominal diameter. These fasteners are used where a flush or low-profile head is required, or where higher clamping force is needed from a smaller head diameter.
**Metric hex nuts (DIN 934 / ISO 4032)**
Standard hex nut height is approximately 0.8 times the nominal diameter. Thin nuts (DIN 439 / ISO 4035) are approximately 0.5 times nominal diameter. Nyloc nuts (DIN 985) add a nylon insert for vibration resistance.
### Corrosion resistance comparison
In order of increasing corrosion resistance for stainless steel fasteners: 410 (least resistant, moderate general corrosion resistance), 304/A2 (good general corrosion resistance, poor in chloride environments), 316/A4 (excellent, including chloride and marine environments), 17-4 PH (good to excellent, varies with heat treatment).
For outdoor applications without salt exposure, 304 is sufficient. For coastal, marine, or chemical environments, 316 is the minimum recommendation. For high-strength applications in corrosive environments, 17-4 PH is the appropriate choice despite the cost premium.
### Torque specifications
Recommended installation torque values for stainless steel fasteners (A2-70, dry assembly):
M6: 9.0 Nm. M8: 21.7 Nm. M10: 43.5 Nm. M12: 75.0 Nm. M16: 183.0 Nm. M20: 357.0 Nm.
These values are for dry assembly. Lubricated assembly reduces required torque by approximately 25-30%. Always verify torque specifications against the engineering requirements for your specific application.
Important: Stainless steel fasteners are susceptible to galling (cold welding) during installation, especially when tightened at high speed. Use anti-seize compound or wax-based lubricant on threads to prevent galling. This is particularly important for 316 stainless steel.
### Structuring fastener data for AI procurement
If you are a fastener supplier, the specifications above represent the type of data that AI procurement systems need from your catalog. Every product record should include the fastener type, nominal size, length, material grade, finish, thread specification, applicable standard, mechanical properties, and pricing at defined quantity breaks.
Suppliers who structure their fastener catalogs with this level of detail become the preferred source for AI procurement agents that need exact specification matching. An agent searching for "hex bolt M10 x 40mm A2-70 DIN 933" will find and purchase from the supplier who has that exact record in their structured catalog.