How to read a mill test certificate for fasteners — and what to specify before you order

Two suppliers can both say "yes, we provide mill certificates" and send you documents with completely different evidentiary value. One may be a signed statement that the goods meet the order. The other may carry measured chemistry and mechanical results traceable to the specific batch in your warehouse.

The difference is defined by a standard, it costs different amounts of money, and it is almost never specified on the purchase order. This page is about closing that gap.

What the document is, and its other names

A mill test certificate records what a material actually is: its chemical composition, its mechanical properties, the grade and standard it was produced to, and the batch it came from. Its function is traceability — the ability to connect a part in your hand to the production batch it came out of.

You will see the same document called several things, which causes avoidable confusion:

• MTC — mill test certificate
• MTR — mill test report
• CMTR — certified mill test report
• Material certificate or inspection document — the term EN 10204 itself uses

These names do not reliably tell you the evidentiary level. The type number does.

The four EN 10204 types

EN 10204 is the European standard that defines inspection documents for metallic products. The 2004 revision leaves four types in use. They are ordered by how much independence and batch-specific evidence they carry.

Type	What it is	Test results?	Who signs it
2.1	Declaration of compliance	None	The manufacturer
2.2	Test report	Yes, but from non-specific production — not necessarily your batch	The manufacturer
3.1	Inspection certificate	Yes, from the specific batch supplied	An inspection representative independent of the manufacturing department
3.2	Inspection certificate, independently validated	Yes, from the specific batch supplied	As 3.1, and countersigned by a third party or the purchaser's representative

The practical line sits between 2.2 and 3.1. A 2.2 tells you what this product generally looks like. A 3.1 tells you what your batch measured. If you ever need to investigate a field failure, only the second one is useful.

Type 2.1 is common and legitimate for standard commodity fasteners in non-critical applications. It becomes a problem only when a buyer believes they bought a 3.1 and received a 2.1 — which is what happens when the order says "with mill cert."

Field by field: what to actually check

When a certificate arrives, work through it in this order. Most problems are found in the first three rows.

Field	What you are checking
Heat / lot number	That it exists, and that it matches the marking on the packaging you received
Standard and grade	That it is the standard you ordered to — not a similar one
Certificate type	2.1 / 2.2 / 3.1 / 3.2, stated explicitly on the document
Chemical composition	Each element inside the range the standard allows
Mechanical properties	Tensile, yield, elongation, hardness — as required by the grade
Property class	For carbon and alloy steel bolts, screws and studs this is defined by ISO 898-1
Coating / surface treatment	Stated, with salt spray hours if you specified them
Issuing party and signature	Who signed, and whether they are independent of production
Country of melt and pour	Where the steel was originally melted and poured — see below

A certificate that lists results but omits the heat number is not doing the one job a certificate exists to do.

The heat number is the field that matters most

The heat number identifies the batch of steel the material came from. It is the thread that connects everything else: through it, a finished fastener can be traced back to a specific melt, and that melt's chemistry and properties.

It matters in exactly the situation nobody plans for. A fastener fails in the field. You need to know whether the rest of that batch is at risk, which shipments contained it, and which of your customers received them. Without a heat number you cannot scope the problem, so the only safe answer is to treat everything as suspect.

So the question to ask a supplier is not "do you provide certificates." It is: from a finished part in a box, can you trace back to the raw material batch — and how long does that take you? The answer separates suppliers who file documents from suppliers who run traceability.

Country of melt and pour

For steel and steel derivative products entering the United States, the country where the steel was originally melted and poured has become a reporting field that importers deal with directly. The location of melt and pour is customarily identified on mill test certificates, which is why this has become a document question rather than only a customs question.

The practical supplier question is simple and worth asking before you place an order: can you state the country of melt and pour for the material you would ship us, and is it documented on the certificate?

What to write in your purchase order

Most certificate disputes are specification failures, not supplier failures. These five lines prevent nearly all of them:

1. The certificate type, by number — for example "EN 10204 Type 3.1"
2. The standard and grade the goods are to be produced and certified to
3. That the heat number must appear on the certificate and on the packaging
4. Whether country of melt and pour must be stated on the document
5. When the certificate is due — with the shipment, or before it ships

The fifth line is the one buyers forget, and it is the one that causes goods to sit at the port. A certificate that arrives two weeks after the container does has already failed at its job.

Frequently asked questions

Is a 3.1 certificate always better than a 2.1?

It carries more evidence, but "better" depends on what you are buying. For a standard commodity fastener going into a non-critical assembly, a 2.1 declaration of compliance is a normal and accepted commercial practice, and insisting on 3.1 for everything adds cost without adding safety. The failure mode is not choosing 2.1 — it is believing you have 3.1 when you do not. Decide the level per application, then write it on the order.

What is the difference between 3.1 and 3.2 in practice?

Both contain actual test results from the batch supplied. A 3.1 is validated by the manufacturer's own inspection representative, who must be independent of the manufacturing department. A 3.2 is additionally countersigned by an independent third party or by the purchaser's own representative. The extra cost and lead time of a 3.2 buys independence from the manufacturer entirely, which is why it appears in regulated and safety-critical work rather than in general industrial supply.

Does the certificate prove the parts in the box are the parts on the paper?

Not by itself. A certificate is evidence about a batch; matching that batch to the physical goods is a separate step. That is what the heat or lot number is for — it should appear on both the document and the packaging so that receiving inspection can reconcile them. If your process files certificates without ever checking them against the labels on the cartons, the documents are not doing anything.

Which standard defines the property classes for steel fasteners?

For bolts, screws and studs made of carbon steel and alloy steel, mechanical and physical properties are specified in ISO 898-1, which sets out the property classes and the properties associated with each when tested at ambient temperature. When a certificate quotes a property class, that is the standard it refers back to. Stainless steel fasteners are covered by a different part of the series.

References

• EN 10204 Certificate Types — definitions of types 2.1, 2.2, 3.1 and 3.2
• ISO 898-1:2013 — Mechanical properties of fasteners made of carbon steel and alloy steel — property classes for bolts, screws and studs
• CSMS #62582900 — GUIDANCE: Section 232 Melt and Pour Requirements — U.S. Customs and Border Protection, issued 9 October 2024. Later guidance has revised this; confirm current requirements with your broker.