Stainless Steel Fasteners
Giriraj Impex is a manufacturer, stockist, supplier and exporter of stainless steel fasteners – stud bolts, hex bolts, heavy hex nuts, washers, threaded rods and special fasteners. We manufacture stainless steel fasteners to ASTM A193 B8 and B8M (Class 1 and Class 2) with ASTM A194 Grade 8 and 8M nuts for pressure bolting, and to ISO 3506 property classes A2 and A4 for general and structural use.
Stainless fasteners are chosen where carbon steel bolting would rust – stainless and duplex flanges, food and pharmaceutical plants, water treatment, marine and coastal installations – and where the joint must stay easy to dismantle after years in service.
Grades and standards
| Standard | Grade / class | Material | Use |
|---|---|---|---|
| ASTM A193 | B8 Class 1 and 2 | 304 | Studs and bolts for pressure and temperature service |
| ASTM A193 | B8M Class 1 and 2 | 316 | As B8, with better chloride resistance |
| ASTM A193 | B8T, B8C | 321, 347 | Stabilised grades for elevated temperature |
| ASTM A194 | Grade 8, 8M | 304, 316 | Heavy hex nuts for B8 and B8M studs |
| ASTM A320 | B8, B8M | 304, 316 | Bolting for low-temperature service |
| ISO 3506-1 / -2 | A2-50, A2-70, A2-80; A4-50, A4-70, A4-80 | 304 type (A2), 316 type (A4) | Metric bolts, screws, studs and nuts for general and structural use |
Class 1 and Class 2 – what is the difference?
In ASTM A193, Class 1 B8 and B8M bolting is carbide solution treated, giving the lowest strength but the highest corrosion resistance. Class 2 is carbide solution treated and then strain hardened by cold work, which raises the strength considerably, especially in smaller diameters, at some cost in corrosion resistance. Class 1 is the usual choice for low-pressure and corrosion-critical joints; Class 2 is chosen when the bolting must carry higher loads, for example to seat spiral wound gaskets on higher-class flanges. The class must be stated on the order.
| Grade | Tensile, MPa (ksi) | Yield, MPa (ksi) | Elongation, % | Reduction of area, % | Hardness max, HBW |
|---|---|---|---|---|---|
| B8 Class 1 | 515 (75) | 205 (30) | 30 | 50 | 223 |
| B8M Class 1 | 515 (75) | 205 (30) | 30 | 50 | 223 |
Class 2 properties depend on diameter and are as given in the standard.
ISO 3506 property classes
Metric stainless fasteners are marked with the steel group and property class, for example A2-70 or A4-80. The number is one tenth of the minimum tensile strength in MPa.
| Property class | Tensile strength min, MPa | 0.2% proof stress min, MPa |
|---|---|---|
| A2-50 / A4-50 | 500 | 210 |
| A2-70 / A4-70 | 700 | 450 |
| A2-80 / A4-80 | 800 | 600 |
A2 corresponds to 304-type steel and A4 to 316-type steel; A4 is preferred for coastal and chloride exposure.
Products and dimensions
- Stud bolts – fully threaded, with two heavy hex nuts, to ASME B18.31.2; lengths for flanges from ASME B16.5.
- Hex bolts and nuts – ASME B18.2.1 and B18.2.2; ISO 4014, ISO 4017, ISO 4032; DIN 931, 933, 934.
- Washers – plain and spring, to ASME and DIN standards.
- Threaded rods, U-bolts, anchor bolts and special fasteners to drawings.
Threads are UNC or 8UN for inch fasteners and metric coarse or fine for ISO fasteners.
Avoiding galling
Stainless threads can gall – the surfaces cold-weld and seize – when nuts are tightened quickly or under high load. Using an anti-seize compound, tightening at a steady speed, avoiding over-torque, and pairing slightly different hardnesses (for example Class 2 studs with Grade 8 nuts) all reduce the risk. For critical joints, PTFE-coated or silver-plated nuts can be specified. Please mention any coating or lubrication requirement on the order.
Manufacturing and inspection
Fasteners are made from stainless bar by hot forging or cold heading, with threads rolled or cut, and heat treated or strain hardened to the class ordered. Each lot is checked for dimensions, threads and marking – every stud end or bolt head carries the grade symbol required by the standard. Fasteners are supplied with mill test certificates (MTC), and third-party inspection is available on request.
Ordering
Please give the product, grade and class, diameter and thread, length, nut grade, quantity and coating – or the flange size, class and number of flanges, and we will work out the bolting.
Applications and related products
Stainless steel fasteners bolt stainless steel flanges and valves in chemical, pharmaceutical, food and water plants, secure equipment and structures in coastal and marine environments, and hold together process skids built from seamless pipes, welded pipes, tubes and pipe fittings. They are made from stainless steel round bars and wires. Our stainless range also includes plates, sheets, coils, circles, rings, angles, channels and flats. See all fastener materials on the fasteners page and grade details on the stainless steel page.
Frequently Asked Questions
B8 is made from 304 stainless steel and B8M from 316, which contains molybdenum. B8M has better resistance to pitting in chloride environments such as seawater and coastal air.
ASTM A194 Grade 8M heavy hex nuts are normally used with B8M studs, and Grade 8 nuts with B8 studs, so stud and nut have matching corrosion resistance.
A4 is the ISO 3506 steel group for 316-type stainless steel and 70 is the property class, meaning a minimum tensile strength of 700 MPa. A2-70 is the equivalent for 304-type steel.
Class 2 is strain hardened for higher strength and is used where the joint needs a higher bolt load, such as higher-class flanges or spiral wound gaskets. Class 1 has lower strength but higher corrosion resistance.
Use an anti-seize compound, tighten at a steady speed without over-torquing, and consider coated nuts or different hardnesses for stud and nut. These steps greatly reduce the risk of threads seizing.
Annealed 304 and 316 are essentially non-magnetic, but cold heading, thread rolling and strain hardening can make finished fasteners slightly magnetic. This does not affect their corrosion resistance.
Request a Quote for Stainless Steel Fasteners
Tell us the product, grade, size, standard, quantity and delivery location, and our sales team will reply with a quotation.