ASTM A194 vs A563 — Nut Standard Comparison Guide
ASTM A194 and ASTM A563 are the two main U.S. nut standards. A194 covers nuts for high-pressure/high-temperature service (refinery, petrochem, valves); A563 covers nuts for structural and general bolting (building, bridge, machinery). This page compares both standards side-by-side.
Standard Scope Comparison
| Aspect | ASTM A194 | ASTM A563 |
|---|---|---|
| Full title | Carbon and Alloy Steel Nuts for Bolts for High-Pressure or High-Temperature Service | Carbon and Alloy Steel Nuts (general) |
| Service | High-pressure / high-temperature bolting | Structural and general bolting |
| Common pairing | ASTM A193 stud bolts | ASTM A325, A490 structural bolts |
| Grade range | Grades 1-16 carbon/alloy + 8-9 stainless | Grades A, B, C, D, DH, O |
| Heat treatment | Quenched and tempered (most grades) | Q&T (DH); annealed/normalized (others) |
| Hardness control | Tight (refinery/petrochem service) | Standard structural ranges |
Grade Equivalence
| A194 Grade | Equivalent A563 Grade | Notes |
|---|---|---|
| Grade 2H | Grade DH (most common) | Both Q&T carbon steel; DH is structural variant |
| Grade 2 | Grade B or C | Q&T medium-carbon steel |
| Grade 4 | Grade DH3 | Alloy steel Q&T (rare in A563) |
| Grade 7 | None direct | A563 doesn't cover Cr-Mo alloy (use A194 7 for B7 pairing) |
| Grade 8 (304 SS) | F593 stainless | F593 is separate stainless standard |
When to Specify A194
- Refinery, petrochemical, valve flange bolting
- Pressure-vessel and boiler bolting
- High-temperature service (above 250°F / 121°C)
- Paired with ASTM A193 stud bolts
- Code-required service (ASME B31.3, B31.1, B16.5)
When to Specify A563
- Structural steel construction (buildings, bridges)
- Paired with A325 or A490 high-strength structural bolts
- Galvanized service (A563 covers hot-dip galvanizing requirements)
- Machinery and equipment assembly at ambient temperature
Common Cross-Substitution
A563 Grade DH and A194 Grade 2H share the same Q&T carbon steel and similar hardness range, so they're often considered interchangeable for non-critical bolting up to 800°F. However, refinery/petrochem specifications typically REQUIRE A194 2H (not DH) for pressure-vessel and flange service due to A194's tighter inspection requirements.
For the full A194 specification: ASTM A194 PDF. A194 grade pages: 2H · 2HM · 8 · 8M. A194 hub.