What a grade does and does not tell you
| Property | Does the grade tell you? |
|---|---|
| Strength class of the bolt material | Yes, in general; the head marking shows the class |
| Correct bolt head and shank shape for your edge holes | No; check the edge and moldboard specification |
| Correct tightening torque for your joint | No; depends on size, thread, lubricant and the maker’s spec |
| Behaviour under repeated impact | Not directly; ask the maker |
| Corrosion resistance | No; depends on plating or coating |
Questions to ask the maker or supplier
The bolt questions are decided by the joint, not by the bolt catalogue.
- Which bolt, size, head style and grade do you specify? Ask for the combination, not one attribute of it.
- What torque should I use, and for dry or lubricated threads? The number is meaningless without the friction condition.
- Is there a reason for the grade? Some joints rely on the bolt yielding; others need it to stay elastic.
- What nut and washer go with it? A matched nut keeps the failure in the bolt rather than in the thread.
- Is any plating or coating specified? Coating changes friction, and friction changes torque.
What to check on the bolts you have
You cannot manage what you cannot identify, and bolt grade is the first thing to disappear in a mixed bin.
- Look at the head markings and record them for a sample of your bolts. The markings are the only reliable identification once the box is gone.
- Check whether the markings are consistent across a box, and ask the supplier if they are not. Mixed grades in one box are a common supply problem.
- Keep different grades in separate, labelled bins. Mixing is how an 8.8 ends up where a 10.9 was specified.
Why mixing causes trouble
A stray bolt of the wrong type can sit in a joint unnoticed. If the joint then loosens or fails, you will not know whether the cause was the bolt, the torque or the edge. Marking and bin discipline remove that uncertainty.
Limits
This article gives no strength values or torque figures. Take them from the maker’s documents and the relevant standard.
Boundary: No strength, torque or standard value is cited because the bolt standard was not read; use the plow maker’s specification and the standard itself.
Further reading on this site.
Can we use a carbide grade developed for machining as a snowplow insert grade? ↗Can a blade trial continue after the supplier changes the insert grade? ↗Carbide snow plow blades ↗Anti-Seize on Plow Bolts: It Helps Removal and Changes the Torque Question ↗Ceramic-Insert Blades: Why Agency Reports Were Mixed ↗Painted or Bare Edges in Transit: What Corrosion Protection Is Reasonable ↗
