JMIKS Fasteners supplies SS 304 fasteners: bolts, screws, nuts, washers, studs and special bolts. We are a fastener wholesaler and supplier in Nava Odhav, Ahmedabad, since 2014. SS 304 is the standard stainless steel for fasteners: it resists rust in most everyday conditions and costs less than SS 316.
SS 304 is an austenitic stainless steel with nominally 18 % chromium and 8 % nickel, hence the name 18/8 stainless. Typical limits are 17.5 to 20 % chromium, 8 to 10.5 % nickel, up to 2 % manganese and up to 0.08 % carbon. The chromium forms a thin oxide film that re-forms by itself in air when scratched. SS 304 cannot be hardened by heat treatment; fasteners gain strength from cold forming.
Stainless bolts are marked to ISO 3506-1. “A” means austenitic, “2” is the steel group that covers SS 304, and the number after the dash, multiplied by 10, is the minimum tensile strength in MPa.
| Marking | Condition | Min tensile strength | Min yield (0.2 % proof) strength |
|---|---|---|---|
| A2-50 | Not cold worked (soft) | 500 MPa | 210 MPa |
| A2-70 | Cold worked: the usual class for bolts | 700 MPa | 450 MPa |
| A2-80 | Strongly cold worked | 800 MPa | 600 MPa |
The marking, for example A2-70, sits on the bolt head with the maker’s mark. Nuts to ISO 3506-2 are marked the same way.
SS 304 does not rust in normal air, rain, fresh water, steam, most foods and many mild chemicals. Its weak point is chloride, which breaks the oxide film in small spots (pitting) and attacks tight gaps under washers and in threads (crevice corrosion). Above about 60 °C, chlorides can also crack stressed parts (stress corrosion cracking). Brown spots on new parts are usually iron dust from nearby grinding; a stainless steel cleaner removes them.
Good uses:
Avoid SS 304 for:
Galling is cold welding of threads during tightening: pressure wipes off the oxide film, the clean metal sticks, and the nut locks, often for good. SS 304 galls far more easily than carbon steel. To prevent it:
Annealed SS 304 is non-magnetic. Cold forming turns part of it into magnetic martensite, so finished bolts and nuts often pull lightly on a magnet. This is normal, not a sign of a lower grade. A magnet cannot confirm the grade either way; only a chemical test can.
| SS 304 | SS 202 | SS 316 | |
|---|---|---|---|
| Nickel | 8 to 10.5 % | 4 to 6 % | 10 to 14 % |
| Manganese | up to 2 % | 7.5 to 10 % | up to 2 % |
| Molybdenum | none | none | 2 to 3 % |
| Rust resistance | Good: general outdoor | Fair: indoor and dry | Excellent: marine and chemical |
| Fastener marking | A2 | Not in ISO 3506 | A4 |
| Relative cost | Medium | Lowest | Highest |
Our SS 304 vs SS 316 vs SS 202 guide has more detail.
All are listed in SS 304, and most also in SS 316 and SS 202.
Sizes: M3 to M36 and 1/4″ to 1-1/4″ BSW; each product page gives its exact range.
A2 is the ISO 3506 marking for 18/8 austenitic stainless steels, of which SS 304 is the most common. SS 304 bolts are usually marked A2-70.
Not in normal air and water. Near the sea, in pool water or with bleach it can pit and stain, so use SS 316 there. Brown spots on new parts are usually iron dust and clean off.
No. A2-70 has 700 MPa minimum tensile and 450 MPa yield strength, against 800 and 640 MPa for 8.8. A2-80 reaches 800 MPa but yields at 600 MPa. For heavy loads, use high tensile bolts.
Use SS 304 nuts and washers. Mixing stainless with zinc plated or galvanized parts can cause galvanic corrosion in wet places. Anti-seize on the thread stops galling.
SS 202 costs less and suits dry indoor fittings and furniture. For kitchens, bathrooms, damp areas or outdoors, choose SS 304, as SS 202 can show rust spots there.
Send the product, size, grade and quantity on WhatsApp +91 90333 11425, use our enquiry form, or download the catalogue (PDF). We reply within one working day, Monday to Saturday, 10 am to 8 pm.
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