Buyer guide
Prepared by LD Screw · Reviewed · Practical guidance for fastener RFQ preparation.
Material and strength are separate purchasing decisions. A dimensional standard defines shape and size, while a material grade or property class defines mechanical or corrosion-related requirements. Write both into the inquiry so appearance is not used as a substitute for specification.
Common material and grade references
The descriptions below are procurement starting points. The governing standard, test method and required documentation must be confirmed for the actual order.
| Reference | Typical purchasing direction | What to confirm |
|---|---|---|
| Carbon steel | General bolts, nuts, screws and fabricated fasteners | Product standard, property class, heat treatment and finish |
| Property class 8.8 | Metric bolts for machinery and general steel assemblies | ISO 898-1 requirement, size, thread, coating, marking and test documents |
| Property class 10.9 / 12.9 | Higher-strength metric bolts and socket screws | Application design, heat treatment, coating restrictions and verification |
| A2 / 304 stainless | General corrosion-resistant fasteners | Exact stainless grade, property class, environment and surface condition |
| A4 / 316 stainless | Projects needing improved chloride-related corrosion resistance | Grade, property class, exposure, mating parts and documentation |
How to read a metric property class
For a bolt marked 8.8, the first number relates to nominal tensile strength and the second number relates to the yield-strength ratio. This is a mechanical classification, not a dimensional standard and not a coating specification.
Nut classes, washer requirements and structural bolting systems use their own references. Do not assume that every component in an assembly is covered by the bolt marking.
- State the dimensional standard separately, such as ISO 4014 or ISO 4017
- State whether testing, inspection records or traceability are mandatory
- Check whether the selected coating can affect threads or high-strength material
- Specify compatible nuts and washers instead of requesting an unspecified set
Material information for a useful RFQ
Include the service environment and the reason for the selected material. This helps identify missing requirements before price is discussed.
- Product standard or dimensioned drawing
- Material grade and bolt property class where applicable
- Diameter, pitch, length, quantity and mating components
- Surface treatment, corrosion environment and operating temperature if relevant
- Required certificate, test, marking, labeling and export packing