If you have ever bought stainless fixings, you may have seen A2 printed on the box or stamped on the heads. It is the most common grade of stainless steel used for nuts, bolts and screws, and most of the time it is the right choice. But A2 comes with its own little code, A2-70 and the rest, plus a fair bit of confusion about whether it is the same thing as 304 or 18/8.
This page sorts all of that out in plain language. What A2 stainless steel actually is, whether it rusts, and how to read the grade numbers before you order.
What is A2 stainless steel?
A2 is a grade of austenitic stainless steel used to make fasteners. It is the fixings-trade name for the everyday stainless that holds together everything from garden furniture to kitchen kit.
Any steel needs at least 10.5% chromium to count as stainless. That chromium reacts with the air and forms a thin, invisible layer on the surface, and that layer is what fights off rust. A2 goes further with roughly 18% chromium and 8% nickel, which is where the old nickname 18/8 comes from.
The grade sits under a standard called ISO 3506, the rulebook for stainless fastener properties. So when you see A2 on a bolt, it is telling you both what the metal is made of and roughly how strong it is.
Austenitic is just the family name for this type of stainless. In plain terms, it means A2 is tough, easy to form and easy to weld, which is a big part of why it ended up everywhere.
A2, 304 and 18/8: are they the same thing?
Near enough, but not exactly. 304 is the material grade you see on sheet, bar and tube. 18/8 is the same steel described by its chromium and nickel content. A2 is the fastener version of that family, defined by the fastener standard rather than the material one.
In Europe you will also see it written as 1.4301, or X5CrNi18-10 if someone is being formal. They all point at the same broad type of stainless. For buying fixings, A2 is the term that matters.
A2 and its equivalents
| Name | What it refers to |
| A2 | The fastener grade, set by ISO 3506 |
| 304 | The material grade for sheet, bar and tube |
| 18/8 | The same steel, named after its 18% chromium and 8% nickel |
| 1.4301 / X5CrNi18-10 | The European (EN) material number for it |
The grade codes: A2-50, A2-70 and A2-80
The number after the dash is about strength, not rust. All three resist corrosion the same way, because they are the same metal. What changes is how hard the steel has been worked, which sets how much load it can take.
A2-70 is the one you will see most often. It is the standard supply condition for stainless bolts and screws, strong enough for general work without being specialist. A2-50 is softer, A2-80 is harder and stronger. The table shows the minimum figures from the standard.
A2 property classes (ISO 3506-1)
| Class | Min tensile strength | Min proof stress | Supply condition |
| A2-50 | 500 MPa | 210 MPa | Soft, annealed |
| A2-70 | 700 MPa | 450 MPa | Cold worked, the usual one |
| A2-80 | 800 MPa | 600 MPa | Harder cold worked |
Which class comes in which size?
The strength classes are set for common sizes, up to and including M24 for A2-70 and A2-80. A2-50 covers a wider size range.
Above M24 the figures are not fixed by the standard; they are agreed between buyer and supplier, and bigger diameters are often supplied a little softer. So treat A2-70 as the typical answer for everyday sizes rather than a rule that holds at every diameter. If strength really matters for your job, check the spec for the exact size you are buying.
For most everyday fixings you will not have to pick a class at all. If a listing just says A2, it is almost certainly A2-70, because that is what stainless bolts and screws are normally made to.
Does A2 stainless steel rust?
Short answer: it can, but for most jobs it will not.
A2 protects itself with that passive chromium layer, and for general indoor and outdoor use it holds up well. Rain, damp, the odd splash, all fine. It is the standard choice for fixings that live outside without being battered by salt.
Where it struggles is prolonged salt or chloride. Coastal air, sea water, swimming pools, heavy road salt, that is where A2 can start to pit and stain over time. For those jobs you want a marine grade like A4, which adds molybdenum for extra resistance. If your fixings will spend their life near the sea, A4 is worth the step up.
One thing that worries people needlessly: a light tea-coloured stain on the surface is usually just tiny bits of ordinary steel picked up during fitting, from a drill or a wire brush. It wipes off, and it is not the stainless itself failing.
Is A2 stainless steel magnetic?
Mostly no. In its soft, annealed state A2 is essentially non-magnetic, which catches people out because they expect steel to grab a magnet.
Once it has been cold worked, and making a bolt involves plenty of that, it can turn slightly magnetic. A fastener that gives a weak tug on a magnet is completely normal. It does not mean you have been sold the wrong thing. It is still A2.
Where A2 gets used
A2 is the default stainless for general fixings, so you find it almost everywhere fasteners are used away from the sea. Garden and outdoor projects, machinery, kitchen and catering kit, food equipment, general engineering and everyday repairs.
It is also the go-to for restorers and hobbyists redoing bikes, cars and old machinery, where the original fixings have rusted solid and A2 replacements will not do the same again.
It gives you good corrosion resistance and sensible strength at a fair price. That mix is exactly why it became the standard.
Buying A2 fixings from Bolt Base
We stock A2 across a wide range of sizes and head types. If you are after socket screws, the A2 socket cap screws collection is the place to start, and there is a broader socket cap screws range if you want to compare head styles.
The useful bit for most people, there is no minimum order. Buy one A2 bolt or a thousand, whatever the job actually needs. If a shop only had them in bags of a hundred and you needed three, that is the gap we fill.
A2 stainless steel FAQ
Is A2 stainless steel rust proof?
No stainless is truly rust proof, and it is more honest to call it rust resistant. A2 shrugs off everyday damp and general outdoor weather, but given enough salt or chloride over enough time it can stain or pit. For normal use it will not let you down. For coastal or marine work, choose a marine grade instead.
Is A2 the same as 316?
No. A2 lines up with 304. 316 is the grade used for marine fixings, so if a job specifically needs 316, A2 is not the one to reach for.
What does the 70 in A2-70 mean?
It is a strength class, not a size or a finish. A2-70 meets a minimum tensile strength of 700 MPa. A2-50 is softer at 500, A2-80 is stronger at 800. The corrosion resistance is the same across all three.
Should I use A2 for a job near the sea?
For general indoor and outdoor use, A2 is the usual pick. Right by the sea or around strong chemicals, it is not the right grade, and a marine grade will last far longer. We are putting together a fuller A2 versus A4 guide for those in-between cases where it is a closer call.
So, which do you need?
A2 is the common 304 and 18/8 stainless used for most fixings. The number after the dash is about strength, not rust, and it copes with everyday weather but not a life by the sea. Get those three things straight, and you will pick the right grade nearly every time.
If you are still not sure whether A2 suits your job, just ask. We would rather help you get the right fixing than sell you the wrong one.