| Point | 8.8 | 10.9 |
|---|---|---|
| General strength level | Lower | Higher |
| Typical use thinking | Common structural and general use | Where a higher clamp load or smaller bolt is wanted |
| Sensitivity concerns | Generally less sensitive to brittle behaviour | Higher-strength fasteners generally call for more care with coatings and processing |
| Cost | Often lower | Often higher |
| Matching nut and washer | Match the class and style | Match the class and style |
These are cautious generalisations, not test results.
Questions for the supplier
Class 8.8 and 10.9 bolts are not interchangeable on a plow edge, and the difference usually shows up as joint failure rather than bolt failure.
- What class and style of bolt do you supply with this edge, and why? Ask for the reasoning, not just the class number.
- What nut and washer are supplied, and are they matched to the bolt? A mismatched nut moves the failure into the thread.
- What finish or coating is on the hardware? Coating changes friction, and friction changes torque.
- What torque do you specify for that hardware? The figure should arrive with the lubrication assumption attached.
- Has this combination been used on routes like mine? Salt exposure and re-torque practice decide whether the joint survives a season.
Things that matter as much as the class
The bolt class is only one of four things that decide whether a joint holds.
- Head and neck style. Carriage or plow bolts have a shape that locks into the edge. Changing to a different head can change how the bolt seats.
- Hole fit. Oversize or worn holes change load paths.
- Corrosion. Salt can seize or weaken any fastener, so washing matters.
- Reuse. Do not reuse bolts that were heated, stretched or heavily rusted.
What to record
When you fit bolts, record the class marking on the bolt head, the nut style, the finish and the torque applied. If you later find loosening, cracking or seizing, that record is the first thing to check, and it is often the only way to see whether a pattern follows one batch of hardware or one position on the edge.
A practical rule
Use the hardware the edge supplier specifies, as a complete set, and replace it with the same specification. If you want to change class, ask the supplier in writing and trial it on one truck.
Boundary: no strength values are quoted because the standard was not read for this article. Check ISO 898-1 and supplier data before specifying fasteners.
Further reading on this site.
Steel Grades for Plow Edges: Hardness, Toughness and Weldability Trade-Offs ↗AASHTO and DIN Bolt Patterns for Plow Edges: Reading the Standards ↗Carbide snow plow blades ↗What Salt-Spray Hours Mean for Plow Hardware: ASTM B117 in Plain English ↗Hard Does Not Mean Tough: Hardness vs Toughness Explained With Plow Examples ↗Standard Carbide-Blade Specs: What Clear Roads Project 17-02 Set Out to Do ↗
