What 8.8, 10.9 and 12.9 mean
ISO 898-1:2013 defines mechanical and physical properties for carbon-steel and alloy-steel bolts, screws and studs with specified property classes. The standard covers coarse and fine metric threads within its stated scope and evaluates the fasteners at an ambient temperature range of 10 °C to 35 °C. In this guide, 8.8, 10.9 and 12.9 are property-class references—not material trade names, product families or stock promises.
The class is only meaningful together with the applicable product, thread, diameter, test and marking requirements. A higher class label does not by itself prove that a bolt is the correct choice for a joint, nor does it replace the drawing, engineering calculation or customer specification.
| Property class | What it signals in an RFQ | What it does not prove |
|---|---|---|
| 8.8 | A specified carbon/alloy-steel property class for the application to review | The required geometry, finish, corrosion performance, traceability or suitability of the joint |
| 10.9 | A higher property-class reference than 8.8 within this comparison | That the assembly, tightening method, hydrogen-embrittlement controls or mating parts are appropriate |
| 12.9 | The highest of the three class labels compared here | Automatic approval for every diameter, temperature, coating, load case or service environment |
Do not select by grade alone
The bolt must work as part of a joint. Confirm the applied load, clamped materials, required preload, tightening method, thread engagement, bearing area, fatigue or vibration exposure and the consequences of failure. Head geometry, diameter, thread pitch, length and grip can change the engineering result even when the property class is unchanged.
ISO 898-1 does not by itself specify every property a project may need. ISO notes that corrosion resistance, resistance to shear stress, torque/clamp-force performance and fatigue resistance require separate consideration. The standard also identifies geometry cases that may not meet its tensile or torsional requirements because of reduced head shear area. For a safety-critical or engineered assembly, route the final selection through the responsible engineer.
Separate class, material, finish and product standard
A product standard identifies geometry or product characteristics; a property-class standard addresses mechanical and physical requirements; a coating or finish requirement addresses the surface system and service environment. Keep those decisions separate in the RFQ. A zinc finish, a black appearance, a socket drive or a familiar catalogue name is not evidence of 8.8, 10.9 or 12.9 compliance.
For socket head cap screws, also identify the governing product reference, such as ISO 4762:2004, and confirm the requested property class separately. For hex bolts, state the requested dimensional standard and revision separately from the class. Do not silently convert a legacy DIN designation or an internal part number.
When to ask for test and traceability evidence
- Applicable product and mechanical-property standard, edition and any customer or drawing revision.
- Material route, heat or lot identification, property class marking and the required inspection or test records.
- Dimensional, thread, hardness, tensile, proof-load or other checks when required by the governing specification.
- Finish or coating designation, service environment, post-treatment controls and any installation constraints.
- Mating nut and washer requirements, packaging, marking, traceability and the approval point before production release.
How to write the comparison into an RFQ
Ask suppliers to quote the requested class as a controlled requirement and to identify any proposed alternative on a separate line. A comparable quotation should state the product standard, class, material, dimensions, finish, quantity, documentation scope and commercial assumptions. If the application could accept more than one class, ask the engineer or customer to define the acceptance rule instead of leaving the choice to the lowest quote.
- Part number or drawing and revision, including the governing dimensional standard.
- Diameter, pitch, length, thread length, head style and required grip or engagement.
- Property class 8.8, 10.9 or 12.9, plus material and required marking or tests.
- Finish, service environment, mating components, installation method and corrosion controls.
- Quantity per size, destination, packaging, traceability and required approval documents.