Guide
What should a certificate of conformance include for machined and cast parts?
A certificate of conformance is a signed statement from the supplier that a specific shipment of parts was made and inspected to the purchase order, the drawing revision and every specification the order invokes. It is a declaration, not a test report: it usually carries no measured data, and its value depends entirely on how precisely it names what it vouches for.
By Saola Manufacturing engineering team · Published · Updated
Buyers often receive three or four documents with a lot of machined or die-cast parts and are not sure which one answers which question. This guide sets out the fields a certificate of conformance (CoC) should carry, how it differs from a certificate of analysis (CoA) and a material certificate, who should sign it, and the purchase-order wording that gets you a useful document instead of a one-line letter. It describes the governing standards and common practice, not the paperwork of any particular supplier.
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What must a certificate of conformance contain?
At minimum: who is declaring, exactly which parts, against exactly which requirements, and who signed on what date. A CoC that leaves out the drawing revision or the lot identity cannot be tied to the parts on your dock, so it proves very little.
The general framework for this kind of declaration is ISO/IEC 17050-1, which sets the content of a supplier’s declaration of conformity: a unique identification of the declaration, the issuer’s name and contact address, the object being declared, the statement of conformity, a complete list of the standards or other specified requirements it covers, the date and place of issue, the signature, name and function of the person authorized to sign, and any limitation on validity. Translated to a lot of machined or cast parts, a complete CoC carries these fields:
- Document number and issuer. A unique CoC number, the legal name and address of the company making the parts, not only a trading name or a broker.
- Order reference. Your purchase order number and line item, so the certificate cannot be reused for a different order.
- Part identity. Your part number and the drawing revision letter exactly as it appears in the title block, plus any approved deviation or engineering change numbers.
- Quantity and lot. The quantity shipped and the lot, batch or date code that also appears on the carton labels and, where the drawing requires it, on the parts.
- Material. Alloy, temper and governing standard, with the heat or lot number of the bar or ingot used and a reference to the material certificate that covers it.
- Processes and specifications. Every specification named on the drawing or PO, with its revision: finish (for example zinc plating with trivalent chromate to the specification the drawing cites), heat treatment, thread standard, cosmetic standard, and any restricted-substance requirement such as EU RoHS Directive 2011/65/EU.
- Outside processing. Which operations were performed by a subcontractor and the subcontractor’s own certificate reference.
- The statement itself. A sentence that the parts conform to all requirements of the order and drawing, with any exception named rather than implied.
- Signature block. Name, title and date of a person with authority to release product, preferably from quality rather than sales.
US federal buyers have used the same structure for decades. The government clause FAR 52.246-15, Certificate of Conformance, prescribes a statement that the supplies conform in all respects with the contract requirements, “including specifications, drawings, preservation, packaging, packing, marking requirements, and physical item identification (part number)”, signed by a responsible official and tied to a shipping document. Commercial buyers do not have to use that wording, but it is a good checklist for what “conforms” should cover.
How does a CoC differ from a CoA and a material certificate?
A CoC declares that finished parts meet the order; a CoA reports measured analysis results for a batch; a material certificate reports chemistry and properties for the heat of metal the parts came from. They answer different questions, and a sourcing file for a machined part usually needs the CoC plus the material certificate.
The confusion comes from the names. “Certificate of analysis” is the usual term in chemicals, plating solutions and alloy ingot, where the document lists a measured composition against limits. In bar and plate the same role is played by the mill test report (MTR), and in Europe by the inspection documents defined in EN 10204. Some suppliers use “CoA” and “material cert” interchangeably; what matters is whether the document carries measured results and whether those results belong to the material you received.
| Document | What it attests | Measured data? | Normally issued by |
|---|---|---|---|
| Certificate of conformance (CoC) | Finished parts meet the PO, drawing revision and cited specifications | No, a declaration | The part manufacturer |
| Certificate of analysis (CoA) | Measured composition or properties of a batch against stated limits | Yes | The producer of the batch (ingot, chemical, plating bath) |
| EN 10204 type 2.1 | Declaration of compliance with the order | No | The material manufacturer |
| EN 10204 type 2.2 / typical MTR | Results typical of the product line, not necessarily the delivered heat | Yes, non-specific | The material manufacturer |
| EN 10204 type 3.1 / heat-specific MTR | Results measured on the delivered heat or lot | Yes, specific | The material manufacturer’s authorized inspection representative, independent of the manufacturing department |
| First article inspection report | Every toleranced drawing feature measured on the first piece from new tooling | Yes | The part manufacturer |
| Certificate of origin | Country of origin for trade and customs purposes | No | An authorized issuing body, or the exporter where a trade agreement allows self-certification |
Read the table as a chain. The material certificate speaks for the metal; the inspection report speaks for dimensions; the CoC speaks for the whole order and points to the other two. A CoC with no reference to a material certificate is asking you to take the alloy on trust. The EN 10204 3.1 vs 2.2 guide explains when a heat-specific certificate is worth requiring.
Many ASTM product specifications also contain a short certification section. In ASTM B211/B211M for aluminum bar, for example, the producer furnishes, on request, a statement that the material was sampled, tested and inspected per the specification and met its requirements. That is a CoC at the material level, and it only exists if the order asks for it.
A certificate of origin is a different category again. It answers a trade question, not a quality one, and for US imports the origin-marking rules in 19 CFR Part 134 look at where the part was last substantially transformed, not where the bar was melted. Keep the origin file and the quality file separate.
Who should sign a certificate of conformance, and what does the signature mean?
The signer should be someone with authority to release product, normally the quality manager or a named delegate, not a salesperson or a freight forwarder. The signature is the supplier accepting responsibility that every requirement on the order was met, including ones you never inspect.
That second point is why the CoC matters even though it holds no data. Most buyers measure a sample of dimensions on receipt and never verify plating chemistry, heat treatment or restricted substances. Those requirements rest on the CoC. If a field failure later traces back to a finish that was not to specification, the signed CoC is the document that shows the supplier declared otherwise.
Three checks on the signature block catch most weak certificates. The signer is named and has a title, not just a stamp. The date is on or after the inspection date and on or before the ship date. And the issuing company is the one on your approved-supplier record. If a trading company issues the CoC for parts made elsewhere, ask for the manufacturer’s own certificate as well, because the trader can only declare what it was told.
Electronic signatures and PDF certificates are widely accepted in commercial supply. If you need a wet signature or an original that travels with the goods, say so on the purchase order; otherwise expect a scan.
What should a CoC cover on a part that is cast, machined and finished?
It should cover the part as delivered, which means every step: the casting or bar stock, the machining, any heat treatment and the finish. Each step that was done by another company should be named on the CoC together with that company’s own certificate.
A die-cast housing that is machined and powder coated, or a turned bushing that is zinc plated, passes through several distinct processes. The risk is a CoC that is true for the step the issuer performed and silent on the rest. A machine shop that sends bar out for plating, for instance, may sign a CoC that covers dimensions only, while the plating specification is backed by nothing more than the plater’s invoice.
Ask the supplier to list on the RFQ reply which steps run in its own plant and which go to partners. For outside steps, the CoC should reference the subcontractor’s certificate, and the supplier should keep that certificate on file against your lot. For die castings, the material line should name the alloy standard, such as ASTM B85/B85M for aluminum die castings, and reference the chemical analysis behind it, either the caster’s own analysis of the melt or castings or the ingot supplier’s certificate for the ingot lots used, because the casting is poured from remelted ingot and returns rather than from a single heat.
Finishes deserve their own line. “Zinc plated” is not a specification. The CoC should name the finish specification and type or class from the drawing, and if the drawing calls for a salt-spray or adhesion test, the CoC should reference the test report rather than restate the result. A CoC that declares conformance to a test that was never run is the most damaging kind of error, because it looks complete.
How should you specify the certificate of conformance on a purchase order?
Write the requirement as a short clause on the PO and the RFQ that names the document, its required fields, the signer and how it is delivered. “C of C required” on its own produces a one-line letter that names no revision, no lot and no specification.
A clause along these lines covers most machined and cast parts:
- “Supplier shall furnish a certificate of conformance with each shipment, signed and dated by an authorized quality representative, stating that the parts conform to this purchase order and to drawing [number] revision [letter], including all specifications referenced on the drawing.”
- “The certificate shall show the PO and line number, part number, quantity, lot or date code, and the material alloy, temper, standard and heat or lot number.”
- “The certificate shall list each specification and revision for finish, heat treatment and testing, and identify any operation performed by a subcontractor, with the subcontractor’s certificate attached or available on request.”
- “Material certificates per EN 10204 type 3.1, or a mill test report for the delivered heat containing the same information, shall accompany the certificate of conformance.”
- “Deviations shall be listed on the certificate with the buyer’s written approval reference; a certificate with no listed deviations is a declaration that none exist.”
- “Certificates shall be emailed before shipment and a copy packed with the goods.”
Put the drawing note to match, so the requirement survives if the drawing is quoted without the PO. A typical note reads: “Certificate of conformance and material certificate required with each lot; see purchase order quality clauses.” If you also want first article or lot inspection data, list those documents separately; a CoC does not imply them. The first article inspection guide covers what that report should contain, and the RFQ package guide lists the rest of the package.
What CoC mistakes most often cause a rejected shipment?
The common failures are a wrong or missing drawing revision, a lot number that does not match the labels, and a blanket statement that covers specifications the supplier never checked. All three are avoidable at the PO stage.
- Revision drift. The drawing moved from revision C to D, the PO was updated, and the CoC template still prints C. Receiving inspection should compare the revision on the CoC with the PO line every time.
- Template certificates. The same text, signer and date appear on every shipment. A CoC should be generated per lot, with the lot’s own quantity and date.
- Missing material link. The CoC names the alloy but no heat or lot, so the attached material certificate cannot be shown to belong to these parts.
- Unlisted outside processing. Plating, heat treatment or anodizing was subcontracted and the CoC does not say so. You discover it during a failure investigation.
- Silent deviations. A dimension was accepted on a phone call and never written down. The CoC still says “conforms in all respects”.
- Wrong issuer. A broker or forwarder signs for parts it did not make or inspect.
None of these needs a new standard to fix. They need the PO clause above and a receiving inspector who reads the certificate against the order instead of filing it.
Which quality documents does Saola list for machined and cast parts?
Saola’s quality page lists the documents it issues: a first-article inspection report on new tooling, a dimensional inspection record with every lot, and a Vietnam certificate of origin (Form B) per shipment. Salt-spray results are listed at first article and on request; material certification, a RoHS declaration and process routing sheets are listed as available on request.
A certificate of conformance worded to your own PO clause is not on that published list as a standard document, so put the clause in the RFQ and the written reply states what will be supplied with each lot. Our lead CNC plant runs CNC milling on ADC12 aluminum and Zamak 3 zinc castings sourced from partner foundries, and surface finishing from a fixed menu is applied by partner plants we manage, so the quote names where the casting, machining and finishing steps a CoC has to cover are done. Finishes outside that menu need to be raised early, so name your finish specification in the RFQ. Saola’s ISO 9001 certification is in progress, not held; if a quality-system certificate is a gate for your approved-vendor list, say so before sending a drawing. When your drawing and document list are ready, send them for a quote.
Frequently asked
Is a certificate of conformance the same as a declaration of conformity?
They do the same job. “Declaration of conformity” is the term in ISO/IEC 17050-1 and in EU product legislation, where it often has a legally fixed format; “certificate of conformance” is the common US commercial and defense term for a shipment-level statement.
Does a CoC replace incoming inspection?
No. It shifts responsibility for the requirements you do not inspect onto the supplier, but it is not evidence of measurement. Keep sampling the dimensions that matter and use the CoC for everything else.
Should a CoC include measured dimensions?
Not usually. Dimensional results belong in an inspection report or first article report that the CoC references. Mixing them makes the declaration harder to read and tempts suppliers to report only the easy features.
Can one CoC cover several part numbers on one shipment?
Yes, if it lists each part number, revision, quantity and lot separately. A single line covering “all parts on this shipment” loses the lot link and is hard to use in a later investigation.
Who keeps the CoC, and for how long?
Both sides should keep it for as long as your quality system or your own customer requires record retention for that part. State the retention requirement in the PO quality clauses if it is longer than the supplier’s default.
Sources
- ISO/IEC 17050-1:2004, Conformity assessment — Supplier’s declaration of conformity — Part 1: General requirements, ISO, 2004
- EVS-EN 10204:2004, Metallic products — Types of inspection documents, EVS (national edition of EN 10204:2004), 2004
- FAR 52.246-15, Certificate of Conformance, Federal Acquisition Regulation, acquisition.gov, accessed October 2026
- ASTM B211/B211M-23, Aluminum and Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire, ASTM International, 2023
- ASTM B85/B85M-25, Aluminum-Alloy Die Castings, ASTM International, 2025
- Directive 2011/65/EU on the restriction of hazardous substances in electrical and electronic equipment (RoHS), EUR-Lex, 2011
- 19 CFR Part 134, Country of Origin Marking, Electronic Code of Federal Regulations, accessed October 2026