Fasteners and springs look like the simplest line on a bill of materials, and they are often bought as if they were. Then a lot of plated bolts fails after assembly, or a spring that measured correctly on arrival loses load in service. In both cases the part matched the catalogue description and still was not the part the design needed.
This article is for engineers and buyers ordering bolts, nuts, screws, washers and springs from Vietnamese makers or stockists. It covers the decisions in order: standard part or special, property class, coating and hydrogen embrittlement, what a spring drawing must say, and how a lot is accepted. Machined pins and turned parts with threads are better treated as machined parts; see CNC machining in Vietnam.
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Standard part or special: two different purchases
A catalogue fastener is bought by its standard designation and may come from a stockist; a special is made to your drawing, needs tooling and needs first-article approval like any other made part.
| Point | Standard (catalogue) fastener | Special fastener or spring |
|---|---|---|
| Defined by | A dimensional standard number, size, length, property class, coating | Your drawing and specification |
| Typical source | Stockist, trader, or a maker running standard sizes | Maker with heading, rolling or coiling equipment |
| Tooling | None for you | Heading dies, rolling dies or coiling set-up for your part |
| Approval | Check against the standard and the certificate | First-article inspection and sample approval |
| Main risk | Wrong class, coating or origin hidden behind a correct name | Drawing silent on load, hardness, coating or test method |
For standard parts, write the full designation: the dimensional standard number (ISO, DIN, JIS or ASME), thread size and pitch, length, property class and coating. A description such as “M10 × 40 hex bolt, zinc” can be satisfied by many different parts.
Ask a stockist who made the parts and in which country. A trader may ship fasteners made elsewhere, which matters for the origin of the goods; see origin and transshipment risk for buyers. Vietnamese makers and stockists that supply Japanese-owned assembly plants often list parts by JIS designation, so if your drawing calls up an ISO or ASME standard, confirm that the part offered is made to your standard and not to its nearest JIS counterpart.
Property class: say it, and match the nut to the bolt
For carbon and alloy steel bolts the strength is fixed by the property class under ISO 898-1, and the nut needs its own matching class under ISO 898-2; stainless fasteners use a different system under ISO 3506-1.
Bolts, screws and studs. ISO 898-1 (the 2013 edition, reconfirmed by ISO) specifies mechanical and physical properties for carbon and alloy steel bolts, screws and studs with metric threads, in property classes such as 8.8, 10.9 and 12.9. Write the class on the drawing or order. It also sets marking rules: hexagon-head bolts within its scope carry the property class and the manufacturer’s identification mark on the head. Ask the maker for its head mark and check it on arrival. An unmarked high-strength bolt is a question to raise before the lot is used.
Nuts. ISO 898-2:2022 covers nuts in property classes 04, 05, 5, 6, 8, 10 and 12, intended to mate with bolts of the ISO 898-1 classes. A bolt of the right class with a nut of the wrong class does not give the joint you designed. Specify the nut class next to the bolt class.
Stainless fasteners. ISO 3506-1:2020 designates stainless bolts by steel group and property class, for example A2-70 or A4-80. The part before the dash (A2, A4) is the steel group; the number after it is the strength class. A2 and A4 are not interchangeable where corrosion resistance matters, and neither is a substitute for a carbon-steel class without an engineering check.
What ISO 898-1 does not cover. The standard does not deal with corrosion resistance, weldability, fatigue resistance or torque and clamp-force performance. Torque and clamp-force testing is covered by ISO 16047. If your assembly is tightened to a torque value, the friction of the coating and lubricant decides the clamp load, so specify the friction requirement or the test, not only the class.
Coating and hydrogen embrittlement
Electroplating a high-strength steel fastener can introduce hydrogen that cracks it after assembly, so the coating specification must name the standard, the coating system and the embrittlement measures — not just “zinc plated”.
The choice of coating is a design decision, and in Vietnam it is also a supply-chain question: plating, zinc flake coating and galvanising are often done by a separate coating shop, not by the fastener maker. Ask who coats the parts and who is responsible for the result.
| Coating route | Standard to name | What to specify | Point to watch |
|---|---|---|---|
| Electroplated zinc or zinc alloy | ISO 4042:2022 | Coating system, thickness, passivation, sealant or top coat | Hydrogen embrittlement on high-strength and case-hardened parts |
| Zinc flake (applied without electrolysis) | ISO 10683:2018 | Coating system, with or without top coat and lubricant | Used especially on high-strength fasteners to avoid internal hydrogen embrittlement |
| Hot-dip galvanised | ISO 10684 | Coating requirements, thread allowance for nuts | Not recommended for small or fine threads |
| Stainless, uncoated | ISO 3506-1 class | Steel group and property class | Contamination and galling, not plating |
Electroplating. ISO 4042:2022 covers electroplated coatings on steel fasteners, mainly zinc, zinc-nickel and zinc-iron systems, and sets requirements and recommendations to reduce the risk of hydrogen embrittlement. The 2022 edition revised those measures for nuts, flat washers and case-hardened screws, and states that its requirements take precedence over general electroplating standards for fasteners. For high-strength parts, ask the coating shop to state the embrittlement measures it applies, such as baking after plating, and to record each batch.
Zinc flake. ISO 10683:2018 covers zinc flake coatings applied without electrolysis, and notes that they are used especially on fasteners of 1,000 MPa tensile strength and above to avoid internal hydrogen embrittlement. If your design uses property class 10.9 or 12.9, compare this route with electroplating before you choose.
Hot-dip galvanising. ISO 10684 covers hot-dip galvanised threaded fasteners. Galvanised bolts need nuts whose threads allow for the coating thickness, so buy galvanised bolts and nuts as matched sets from the same supply chain.
Chemistry restrictions. Some destinations restrict hexavalent chromium in passivation layers. State “Cr(VI)-free” if your market requires it, and confirm the restriction against the current rules of the destination; the declarations to request are covered in quality documents to request from a Vietnamese parts supplier.
💬 We can write the class, coating and test lines into your order and carry them into Vietnamese for both the fastener maker and the coating shop — see sourcing from Vietnam.
What a spring drawing must say
A spring is specified by the load it gives at a working length, not by its dimensions alone; the drawing needs the wire material and standard, the loads, the quality grade and the treatments.
A spring drawing that lists only wire diameter, outside diameter, free length and number of coils lets each spring maker adjust coils to suit its own wire, and the load comes out different. Fix the function first:
- Wire. The wire standard and grade, for example EN 10270-1 for patented cold-drawn unalloyed spring wire, whose grades are coded for static or dynamic duty and tensile level (SL, SM, SH, DM, DH), or the JIS or ASTM spring-wire standard your design uses. Stainless and oil-tempered wires have their own standards; name the one you mean.
- Loads. One or two loads at specified lengths, with tolerances. These control the function; free length then becomes a reference dimension.
- Quality grade. For cold-coiled helical compression springs, EN 15800 sets quality grades with permissible variations on wire diameter, coil diameter, spring force, free length and end squareness. Naming the grade replaces a page of tolerances.
- Ends. Closed, closed and ground, or open; squareness and parallelism where the spring seats.
- Treatments. Stress relieving after coiling, presetting (pressing to solid length so the spring does not settle in service), and shot peening for dynamically loaded springs.
- Coating. If plated, the same hydrogen embrittlement question as for high-strength fasteners applies, because spring wire is hard.
- Coiling direction, solid length and the maximum outside diameter in a bore or minimum inside diameter over a rod.
EN 15800 also describes the tests: static load testing at the specified lengths and a test pressing to solid length. Ask for those results on the first-article report, together with the wire certificate.
Accepting a lot of fasteners
Fastener lots are large and look identical, so acceptance depends on a written inspection procedure, lot traceability back to the wire heat and coating batch, and tests that match the property class.
Agree the procedure in advance. ISO 3269:2019 gives an acceptance inspection procedure for fasteners when purchaser and supplier have no prior agreement, and a reference procedure when conformity is disputed. It is not intended for fasteners for high-volume machine assembly or specially engineered applications; for those, the maker’s own in-process control under a quality assurance system such as ISO 16426 is the expected route. In both cases, write the procedure you want into the order rather than relying on a default.
Define the lot. One lot should mean one designation, one wire heat, one heat-treatment batch and one coating batch. Mixed lots are what make a field failure impossible to trace.
Choose the tests. For property-class bolts: hardness, proof load or tensile testing on full-size parts where size allows, and a check for decarburisation on heat-treated parts. For coated parts: coating thickness at defined points, and the corrosion test method and duration if you require one, agreed in writing. For springs: load at the specified lengths, free length after presetting, and dimensions.
Label and pack by lot. Each box should carry the designation, lot number and quantity. Fasteners are dense, so specify carton strength, pallet loading and moisture protection; corrosion inside a container is a real risk for plain and lightly coated parts.
Sampling for visible defects and packing checks is covered in pre-shipment inspection and AQL. Prices and lead times depend on the part, the material, the coating route and the volume; quotations on identical terms are the only benchmark, and comparing Vietnamese supplier quotations shows how to line them up. If your list also includes forged or welded parts, see forgings from Vietnam and steel fabrication and welding in Vietnam.
For customs, screws, bolts, nuts, rivets and washers of iron or steel fall under HS heading 7318, and springs and leaves for springs under heading 7320. Confirm the full national code before relying on a preferential rate; see Vietnam export proof of origin.
💬 Send us the fastener list or the spring drawing. For each project we find, vet and manage the maker and the coating shop that fit, and arrange lot inspection and export documents. Get in touch.
Frequently asked questions
1. Is “grade 8.8 zinc plated” enough on a purchase order?
No. Add the dimensional standard number, thread and length, the ISO 898-1 property class, the nut class under ISO 898-2, and the coating system with its standard, for example ISO 4042 with the passivation and thickness. Without those, compliant-looking parts can differ widely.
2. Why did plated high-strength bolts crack after assembly?
A common cause is hydrogen embrittlement from the plating process. ISO 4042 sets measures to reduce the risk; zinc flake coatings under ISO 10683 are an alternative used on high-strength fasteners. Ask who did the plating and what embrittlement measures were applied to that batch.
3. Can I mix fasteners from a Vietnamese stockist and a maker in the same assembly?
You can, provided both supply the same designation, class and coating system, and you can trace each lot. Ask the stockist who made the parts; that also matters for origin documents.
4. Which spring dimensions should carry tolerances?
The loads at working lengths should, because they define the function. Name a quality grade, for example under EN 15800 for compression springs, and treat free length and coil count as reference values unless they matter to fit.
5. How do I accept a large fastener lot without testing every piece?
Define the lot as one heat, one heat-treatment batch and one coating batch, agree an inspection procedure in writing (ISO 3269 is the default when nothing else is agreed), and require the test results for that lot before shipment.
Sources: ISO 898-1:2013 (reconfirmed 2025); ISO 898-2:2022; ISO 3506-1:2020; ISO 16047; ISO 4042:2022; ISO 10683:2018; ISO 10684:2004; ISO 3269:2019; ISO 16426:2002; EN 10270-1; EN 15800:2008; Harmonized System headings 7318 and 7320. Checked on 19 October 2026.
More industrial sourcing guides: Forgings From Vietnam: Process, Heat Treatment and Inspection · Steel Fabrication in Vietnam: Welding, Paint and Shipping Size · Rubber Moulded Parts From Vietnam: Seals, O-Rings and Mounts. All guides by category are on the industrial sourcing page.