A2-50, A2-70 and A2-80 Stainless Metric Fasteners (ISO 3506 / ASTM F738M)
The metric 304 bolt: A2 is the 18-8 austenitic group, and the number is the tensile strength in tens of MPa — A2-70 at 700 MPa cold worked is the standard stainless bolt on metric drawings.
What A2 stainless (A2-70) is.
ISO 3506 names stainless fasteners by alloy group and strength. A2 is the 18-8 austenitic group: 304, 304L, 305 and related grades, or 303 when the purchaser approves. The suffix is the minimum tensile strength in tens of MPa: A2-50 is annealed at 500 MPa, A2-70 is cold worked to 700 MPa and A2-80 is strain hardened to 800 MPa in the smaller sizes. ASTM F738M carries the same classes but numbers the 18-8 group A1 (markings F738A, F738D, F738G) and reserves A2 for 321 and 347, so an ISO A2-70 bolt is an F738M A1-70.
We machine A2 bolts, screws, studs and nuts in M1.6 to M36 from certified 304 bar and supply them annealed, cold worked or strain hardened to the class ordered, passivated, with anti-seize or silver-plated nuts on request.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.08 |
| Manganese | Mn | — | 2.00 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 18.0 | 20.0 |
| Nickel | Ni | 8.0 | 10.5 |
| Copper | Cu | — | 1.00 |
Values per ASTM F738M-02 Table 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. 304L, 305 and the other 18-8 alloys are listed in the same table. Note that ASTM F738M numbers this group A1 (markings F738A, D, G) and uses A2 for 321 and 347; ISO 3506 calls the 304 group A2.
Mechanical properties.
| Property class · condition · size | Tensile strength, min (MPa) | Yield strength, min (MPa) | Elongation, min (%, machined specimen) | Hardness (Rockwell) | F738M marking |
|---|---|---|---|---|---|
| A2-50 · AF (annealed) · M6–M36 | 500 | 210 | 30 | B85 max | F738A |
| A2-70 · CW · M6–M20 | 700 | 450 | 20 | B96–C33 | F738D |
| A2-70 · CW · over M20–M36 | 550 | 300 | 25 | B83–C31 | F738D |
| A2-80 · SH · M6–M20 | 800 | 600 | 12 | C23–C36 | F738G |
| A2-80 · SH · over M20–M24 | 700 | 500 | 15 | B96–C33 | F738G |
| A2-80 · SH · over M24–M30 | 650 | 400 | 20 | B93–C30 | F738G |
| A2-80 · SH · over M30–M36 | 600 | 300 | 28 | B89–C28 | F738G |
Values per ASTM F738M-02 Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. ISO 3506-1 gives the same class values; extension and torsional requirements are in the specification.
Specifications that apply.
How A2 stainless (A2-70) ships from Houston.
- Hex and heavy hex bolts and cap screws
- Studs and threaded rod
- Nuts and washers to match
- Machined specials to drawing
A2 stainless (A2-70) fasteners we make.
Every item is manufactured to your drawing or standard in A2 stainless (A2-70), imperial or metric, with an EN 10204 3.1 certificate.
Reading A2-70
A2 is the alloy group, 18-8 austenitic stainless; 70 is the minimum tensile strength in tens of MPa, so an A2-70 bolt is a 304-type bolt at 700 MPa, which it reaches by cold working. A2-50 is the same steel annealed and A2-80 is strain hardened further. The system is ISO 3506; ASTM F738M carries the same numbers but calls the 304 group A1 and the 321/347 group A2, and it is the metric counterpart of the ASTM F593 conditions for inch stainless bolts.
Testing, certification and marking
- Tensile and hardness per lot; full-size testing to the F738M or ISO 3506 tables
- Property class marking, for example A2-70 (F738D under ASTM F738M), and manufacturer's identification on the head
- Certificate of conformance or test report with heat number; EN 10204 3.1 available
- Intergranular corrosion capability per ASTM A262 Practice E for the austenitic groups
A4-50, A4-70 and A4-80 Stainless Metric Fasteners (ISO 3506 / ASTM F738M)
The metric 316 bolt: A4 is the molybdenum-bearing austenitic group for chloride and marine service, and A4-80 at 800 MPa strain hardened is the strongest standard stainless metric fastener.
ASTM A276 bar · ASTM F593 bolts304 Stainless Steel (UNS S30400)
The general-purpose 18-8 stainless: 75 ksi annealed bar, cold-worked bolts to 160 ksi, non-magnetic, and resistant to water, food and most mild chemicals.
ASTM A193 / ASME SA-193ASTM A193 Grade B8 Class 1 (304 Stainless)
304 stainless bolting — Class 1 for corrosion resistance and cryogenic-to-1500 °F service, Class 2 strain hardened to 125 ksi for strength.