A Small Part With a Big Cost of Failure
China produces a large share of the world's bolts, nuts, screws and washers, and the price advantage is real. But fasteners fail quietly: a bolt that is one property class too soft, or a coating that is too thin, will not be noticed at goods-in. It shows up later as a loose joint, a snapped bolt or a rusty structure.
Most fastener problems come from a loose specification, not a dishonest factory. If the purchase order only says "M12 x 50 hex bolt, zinc", the factory will make the cheapest part that matches those words.
1. Specify the Property Class Properly
For metric steel bolts, the property class is defined in ISO 898-1:
- Class 8.8: minimum tensile strength of 800 MPa, yield at 80 per cent of that. Medium-carbon steel, quenched and tempered. The workhorse grade for machinery and structures.
- Class 10.9: minimum tensile strength of 1,000 MPa, yield at 90 per cent. Usually alloy steel such as boron steel or 40Cr, quenched and tempered. Used where joints carry higher loads.
- Class 12.9: used mainly for socket head cap screws, and the most sensitive to hydrogen embrittlement.
Nuts must match (property class 8 or 10 to ISO 898-2), and the bolt head must carry the class marking and the manufacturer's identification mark. Ask for the steel grade and heat treatment process, not only the class.
2. Name the Standard, Not Just the Shape
A "hex bolt" can be made to several standards with different head sizes, thread lengths and tolerances. Name the one you need: ISO 4014 / DIN 931 (partly threaded), ISO 4017 / DIN 933 (fully threaded), ISO 4762 / DIN 912 (socket head cap screws), ISO 4032 / DIN 934 (nuts). Note that some ISO and DIN versions differ in across-flats size, for example at M10, M12, M14 and M22, which matters if your tools or assemblies are set up for one of them.
For imperial fasteners, specify SAE J429 Grade 5 or 8, or ASTM A325 / A490 (now F3125) for structural work.
3. Choose the Coating for the Environment
- Electro-zinc plating with passivation (trivalent, RoHS compliant): low cost, indoor or mild conditions. Specify thickness, typically 5 to 12 microns, and the neutral salt spray hours you expect.
- Hot-dip galvanising (ISO 10684): thick and durable for outdoor structures. Threads must be cut or tapped oversize to allow for it, so specify galvanised nuts to match.
- Zinc flake (such as Geomet or Dacromet type, ISO 10683): strong corrosion resistance with no hydrogen embrittlement risk, preferred for 10.9 and 12.9.
- Black oxide or phosphate and oil: minimal corrosion protection, mainly for indoor use or parts that will be painted.
For class 10.9 and above, electroplating must be followed by baking to relieve hydrogen, or avoided altogether. Write this into the order.
4. Inspection: What We Check Before Shipment
- Raw material: mill certificates for the wire rod, with heat numbers traceable to the batch.
- Dimensions: thread gauges (go / no-go), head height, across-flats, length and thread length against the named standard.
- Mechanical properties: hardness testing on samples from each lot, and tensile or wedge-load tests at a lab for critical orders.
- Coating: thickness measurement and, where specified, a neutral salt spray test report (ISO 9227).
- Markings and packing: class and manufacturer marks on heads, lot labels on cartons, and correct quantities per box.
- Documents: an inspection certificate to EN 10204 3.1 for each lot.
Sampling to an agreed AQL level keeps inspection cost reasonable. See our quality control guide for how AQL works, and why material substitution is the risk to watch on fasteners.
5. Terms, MOQ and Lead Times
LS International quotes fasteners FOB a Chinese port or EXW by default. Standard sizes in common grades are often available within 2 to 4 weeks; special lengths, 10.9 alloy grades or zinc flake coatings typically take 4 to 7 weeks plus sea freight. Fasteners are heavy and low in value per kilo, so mixing several sizes into one container and comparing on landed cost makes a real difference.
The Bottom Line
The cheapest fastener quote is only cheap if the property class, standard and coating are exactly what you specified, and you can prove it lot by lot.
LS International Trading Co., Ltd. has branches in China, the UK, Saudi Arabia, Brazil and Australia. We turn your drawings or parts list into a precise specification, verify the manufacturer, and inspect each lot before it leaves China.
Need bolts, nuts, screws or special fasteners? Send us your parts list with sizes, grades, coatings and quantities, and we will reply with a quote within 48 hours (excluding weekends).