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Grades and composition
Bolting grades by specification, because bolting is bought against a code rather than against a material.
| Stud grade | Material | Matched nut | Service ceiling | Specified for |
|---|---|---|---|---|
| A193 B7 | Alloy steel, Cr-Mo | A194 2H | 454 °C | General high-temperature and high-pressure service |
| A193 B8 | 304 stainless | A194 8 | 538 °C | Corrosive service at moderate temperature |
| A193 B8M | 316 stainless | A194 8M | 538 °C | Chloride-bearing and marine-adjacent service |
| A193 B16 | Cr-Mo-V steel | A194 4 / 7 | 593 °C | Higher temperature than B7, where creep matters |
Why the pairing matters
A stud and a nut are a pair. The nut grade is chosen to match the stud’s strength so the assembly does not strip the thread, and the certificate for the joint has to cover both. Supplying one without the other leaves the pairing to chance.
Coating
| Plain | Default; where the environment allows |
| PTFE | Thread lubrication and moderate corrosion protection |
| Zinc flake | Corrosion protection where galvanic compatibility allows |
Coating affects the torque-preload relationship. If the specification gives a torque value, say which coating it was calculated for.