Fabory offers an extensive range of high-quality fasteners manufactured according to international standards including DIN, ISO, ASME, NF and IFI.
The Fabory assortment includes more than 85,000 fasteners, of which approximately 23,000 are manufactured from stainless steel.
STAINLESS STEEL FASTENERS
Stainless steel fasteners are available throughout Fabory’s product range, including bolts, nuts, screws, washers, maritime hardware, threaded rods, pins, rivets, rivet nuts and security screws. Products are available in a wide variety of diameters, lengths and thread types, including metric, imperial, wood, tapping, trapezoidal and pipe threads.
Stainless steel fasteners are used by customers across industries including:
Boat and shipbuilding
Machine manufacturing
Food processing
Wood construction
Automotive
Steel construction
Offshore
Energy
Water treatment
Maintenance
DIY
TECHNICAL INFORMATION
The term stainless steel covers a wide range of iron-based alloys containing sufficient chromium to form a thin, self-repairing passive oxide layer on the surface. Stainless steels normally contain at least 10.5% chromium and may also include alloying elements such as nickel and molybdenum to modify their corrosion resistance and mechanical properties.
For fasteners, the ISO 3506 series classifies corrosion-resistant stainless steels according to their metallurgical structure. The principal groups include:
Austenitic stainless steel, identified by the letter A
Martensitic stainless steel, identified by the letter C
Ferritic stainless steel, identified by the letter F
Duplex austenitic-ferritic stainless steel, identified by the letter D
Austenitic chromium-nickel stainless steels are the most commonly used materials for general stainless steel fasteners. ISO 3506 includes several austenitic grades, with A2 and A4 being the grades most frequently specified for standard industrial applications.
A2 STAINLESS STEEL
A2 is the most frequently used stainless steel grade for mass-produced fasteners. It is commonly associated with AISI 304 and is often described as 18/8 stainless steel because of its typical chromium and nickel content.
A2 provides good corrosion resistance in normal atmospheric conditions, wet environments and many applications involving oxidising acids, organic acids and alkaline solutions.
A2 should not normally be selected for prolonged exposure to seawater, swimming-pool atmospheres, de-icing salts or other environments containing significant chloride concentrations. It can also be unsuitable for certain non-oxidising acids.
A4 STAINLESS STEEL
A4 is a molybdenum-alloyed austenitic stainless steel commonly associated with AISI 316. It is sometimes described as acid-resistant or acid-proof stainless steel.
The addition of molybdenum gives A4 greater resistance than A2 to pitting and crevice corrosion in chloride-containing environments. Typical applications include coastal locations, marine equipment, chemical processing, swimming pools and aggressive industrial atmospheres.
Standard A4 is not suitable for every highly aggressive environment. Extreme offshore, high-temperature or high-chloride applications may require duplex, super duplex or more highly alloyed super-austenitic stainless steels.
A2 VS A4 STAINLESS STEEL — AT A GLANCE
Comparison of commonly specified A2 and A4 stainless steel fasteners
Property
A2 — commonly associated with AISI 304
A4 — commonly associated with AISI 316
Also known as
18/8, V2A, commonly EN 1.4301
Acid-resistant, V4A, commonly EN 1.4401
Typical chromium content
17–19.5%
16.5–18.5%
Typical nickel content
8–10.5%
10–14%
Typical molybdenum content
Not intentionally added
2–3%
Corrosion resistance
Good resistance in normal atmospheric, wet and mildly corrosive environments
Greater resistance to chlorides, acids, marine conditions and aggressive industrial atmospheres
Normally not suitable for
Seawater, swimming pools, de-icing salts, sustained chloride exposure and certain non-oxidising acids
Extreme offshore or very high-chloride applications where duplex or super-austenitic materials may be required
Property class 50
Minimum tensile strength of 500 MPa
Minimum tensile strength of 500 MPa
Property class 70
Minimum tensile strength of 700 MPa, normally achieved by cold working
Minimum tensile strength of 700 MPa, normally achieved by cold working
Property class 80
Minimum tensile strength of 800 MPa, achieved by cold working
Minimum tensile strength of 800 MPa, achieved by cold working
Magnetic properties
Normally non-magnetic when annealed but may become slightly magnetic after cold working
Normally non-magnetic when annealed but may become slightly magnetic after cold working
Relative cost
Normally the lower-cost option
Often approximately 20–30% more expensive, although the difference varies by product, size and market conditions
Typical applications
General engineering, food-processing equipment, indoor installations, architecture and mild outdoor environments
Marine equipment, coastal construction, chemical processing, offshore installations, swimming pools and water treatment
Rule of thumb: choose A2 for general corrosion resistance in indoor and mild outdoor environments. Choose A4 when chlorides are present, including coastal, marine and swimming-pool environments, or where the fastener will be exposed to chemical processing or an aggressive industrial atmosphere.
The grade and property-class designation provides information about both the stainless steel material and the mechanical strength of the fastener. For example, A2-70 identifies an A2 austenitic stainless steel fastener with a minimum tensile strength of 700 MPa.
Minimum mechanical properties for fully loadable A2 and A4 bolts, screws and studs
Property
A2-50
A2-70
A2-80
A4-50
A4-70
A4-80
Minimum tensile strength
500 MPa
700 MPa
800 MPa
500 MPa
700 MPa
800 MPa
Minimum 0.2% proof stress
210 MPa
450 MPa
600 MPa
210 MPa
450 MPa
600 MPa
Minimum elongation after fracture
0.6d
0.4d
0.3d
0.6d
0.4d
0.3d
Typical condition
Soft
Cold-worked
Cold-worked
Soft
Cold-worked
Cold-worked
Note: In the elongation values, d represents the nominal thread diameter. These are minimum reference values for applicable bolts, screws and studs with full loadability. Product geometry, diameter, thread pitch and the relevant product standard must also be considered.
Property class 50 identifies fasteners in the soft condition. Property classes 70 and 80 are achieved through cold working and are available for appropriate bolts, screws and studs. Stainless steel nuts are covered separately by ISO 3506-2 and should be selected with a compatible grade, property class, thread and nut style.
IMPORTANT — STAINLESS STEEL IS NOT STRENGTH-GRADED LIKE CARBON STEEL
Carbon steel fasteners use property classes such as 4.6, 8.8, 10.9 and 12.9 under ISO 898. Stainless steel fasteners use a different designation system under ISO 3506.
For example, the number 70 in A2-70 indicates a minimum tensile strength of 700 MPa. It should not be interpreted as an equivalent carbon-steel property class. Always compare the actual tensile strength, proof stress, application conditions and applicable product standard rather than comparing class numbers alone.
When should I use A2 instead of A4 stainless steel fasteners?
Use A2, commonly associated with AISI 304 or 18/8 stainless steel, for general corrosion resistance in indoor environments, mild outdoor conditions, food-processing equipment and architectural applications. A2 is normally the most cost-effective stainless steel option and is suitable for many fastening applications where significant chloride exposure is not present.
When should I use A4 instead of A2?
Use A4, commonly associated with AISI 316, where chlorides or more aggressive corrosive conditions are present. Applications include marine and coastal environments, swimming pools, chemical-processing plants, offshore installations, water-treatment facilities and industrial atmospheres containing sulphur dioxide. Its molybdenum content provides greater resistance to pitting and crevice corrosion.
Can I use A2 bolts with A4 nuts or mix stainless steel grades?
A2 and A4 components can be used in the same assembly when their dimensions, property classes, thread specifications and service requirements are compatible. However, the corrosion resistance of the assembly will generally be limited by the less corrosion-resistant A2 component. Mixing the grades does not eliminate the risk of thread galling because both materials are austenitic stainless steels. Read our guide to preventing stainless steel seizing.
Are stainless steel fasteners as strong as carbon steel 8.8?
The grades are not directly interchangeable. A standard A2-70 or A4-70 stainless steel fastener has a minimum tensile strength of 700 MPa, while a carbon steel property class 8.8 fastener has a minimum tensile strength of 800 MPa. A2-80 and A4-80 reach a minimum tensile strength of 800 MPa, but their proof stress, ductility, corrosion behaviour and manufacturing condition still differ from carbon steel 8.8. Where higher carbon-steel classes such as 10.9 or 12.9 are required, an appropriately protected carbon or alloy steel fastener may be more suitable.
Are stainless steel fasteners magnetic?
Austenitic A2 and A4 stainless steels are generally non-magnetic in the annealed condition. Cold working during manufacturing processes such as heading, thread rolling and forming can introduce slight magnetism. This is normal and does not automatically indicate that the material is incorrect. Where magnetic permeability is critical, specify a controlled-permeability product and verify the requirement using supplier data or testing.
SHOP STAINLESS STEEL FASTENERS
Explore the Fabory fastener categories below and use the material filters to select stainless steel A2, A4 or another suitable stainless steel grade.
Stainless Steel Bolts
Hexagon bolts, flange bolts, carriage bolts and other bolting products.