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العربية A Material Test Certificate, often called an MTC or mill test certificate, is one of the most important documents in bolt and nut procurement. It tells buyers whether the material, grade, heat treatment, and test results match the order requirement.
For general hardware, an MTC may not always be requested. For structural steel, machinery, oil and gas, mining, marine, and project supply, it is often mandatory.
The key is not just receiving the certificate. Buyers must know how to read it.
What an MTC Shows
An MTC links the delivered fasteners to tested material or production batches. For bolts and nuts, it usually includes product description, standard, material grade, heat number, chemical composition, mechanical test results, and inspection approval.
Buyers sourcing high-strength fasteners should always confirm whether the MTC matches the actual goods, not only the quotation.
First Check: Product Identity
Match the Certificate to the Order
Start with the basic information. Many document problems begin here.
Check:
- Product name
- Size and thread pitch
- Standard or drawing number
- Grade or property class
- Surface finish
- Quantity or batch number
- Heat number
- Manufacturer name
- Certificate date
If the PO says M20 × 100 class 10.9 hex bolts, the MTC should not describe only “steel fasteners.” The product identity must be specific.
For common bolts and nuts, buyers can compare standard fasteners before confirming certificate requirements.
Reading Chemical Composition
What the Elements Tell You
Chemical data confirms whether the steel chemistry is suitable for the specified grade. It does not prove final strength by itself, but it is the first sign of material suitability.
| Element | Why Buyers Check It |
|---|---|
| C — Carbon | Affects strength and hardenability |
| Mn — Manganese | Supports strength and heat treatment response |
| Cr — Chromium | Improves hardenability and corrosion behavior in alloy or stainless grades |
| Mo — Molybdenum | Helps strength retention and alloy performance |
| Ni — Nickel | Important in stainless and special alloy materials |
| S / P — Sulfur / Phosphorus | Usually controlled because excessive levels may reduce toughness |
For stainless steel fasteners, chemical data is especially important. A2, A4, 304, 316, and duplex grades should not be judged by appearance.
Reading Mechanical Data
Strength Results Must Match the Grade
Mechanical data shows whether the finished bolt or nut meets the required performance level.
| Test Item | Common Meaning | Buyer Concern |
|---|---|---|
| Tensile strength | Maximum stress before fracture | Bolt strength verification |
| Yield strength | Stress where permanent deformation begins | Load-bearing performance |
| Proof load | Controlled load without permanent damage | Bolt or nut service safety |
| Hardness | Surface or core hardness range | Heat treatment stability |
| Elongation | Ductility during tensile testing | Brittle failure risk |
| Wedge tensile test | Bolt head and shank integrity | Important for high-strength bolts |
For bolts, screws, and studs, mechanical properties should match the relevant property class or project standard. For nuts, proof load and hardness are often more important than tensile strength alone.
Do Not Ignore Heat Number Traceability
The Heat Number Is the Link
The heat number connects the raw material, production batch, test report, and packed goods. If the carton label, packing list, and MTC do not share traceable batch information, the document becomes weak.
Buyers should ask the supplier to keep heat number traceability for project orders, especially when certificates are required for customs, site acceptance, or third-party inspection.
For custom bolts, anchors, studs, or drawing-based nuts, use custom non-standard fasteners and confirm traceability before production.
Coating Data and Final Condition
An MTC often focuses on material and mechanical data. But coating can also affect acceptance.
For zinc plating, hot-dip galvanizing, zinc flake, black oxide, PTFE, or other finishes, buyers may need a separate coating report. This may include coating thickness, appearance, salt spray test, or hydrogen embrittlement baking record.
For finish selection, review various coated fasteners before confirming the RFQ.
Buyer Checklist for MTC Review
Before accepting the document, check:
- Does the product description match the PO?
- Does the grade match the drawing or standard?
- Is the heat number shown clearly?
- Are chemical values complete?
- Are mechanical test results listed?
- Are results within the required limits?
- Is the certificate signed or approved?
- Does the MTC match packing labels and batch records?
For full sourcing planning, buyers can review the complete fastener products range.
Final Advice
An MTC for bolts and nuts should be read as evidence, not decoration. Chemical data confirms material identity. Mechanical data confirms performance. Heat number traceability connects the certificate to the actual goods.
The safest buying practice is simple: define the certificate requirement before production, then check the MTC against the PO, standard, batch label, and inspection report before shipment.