Grades stocked: A · DH · DH3
Scope
ASTM A563 / A563M covers carbon and alloy steel nuts for general structural and mechanical applications. It is the structural-bolt nut standard and the default pairing for F3125, F1554, A307, and A449 bolting. Grades are distinguished by material, heat treatment, and hardness.
A563 is the carbon/alloy counterpart to A194 (high-pressure/temperature) and F594 (stainless). The two standards overlap for some grades, and A194 2H is an explicitly permitted substitute for A563 DH on F3125 Type 1 bolts.
Grades
| Grade | Material | Typical pairing | Styles available |
|---|---|---|---|
| O | Low-carbon | A307 Grade A (light duty) | Hex, hex jam |
| A | Low-carbon | A307, F1554 Gr 36 & 55, A449 | Hex, heavy hex, heavy hex jam |
| B | Low-carbon, higher strength | A307 Grade B, A449 | Hex, heavy hex |
| C | Medium-carbon | A449, F1554 Grade 105 | Heavy hex |
| C3 | Weathering | A325 Type 3, F1554 Grade 105 weathering | Heavy hex |
| D | Carbon, Q&T | A449, A354 Grade BC | Heavy hex |
| DH | Carbon, Q&T, higher hardness | F3125 A325, A490 (Type 1), A354 BD | Heavy hex |
| DH3 | Weathering, Q&T | F3125 A325, A490 Type 3, A354 BD weathering | Heavy hex |
Styles: hex, heavy hex, hex jam, heavy hex jam, and heavy hex flange. For structural bolting, heavy hex is required — standard hex does not satisfy F3125 assembly requirements.
Mechanical properties — key grades
Grade A (heavy hex, 1/4" – 1-1/2")
- Proof load stress: 90 ksi
- Hardness: 68–32 HRC (approximate; size-dependent)
- Suitable for: Bolts through Grade 5 strength class; F1554 Gr 36 and 55
Grade DH (heavy hex, all sizes up to 1-1/2")
- Proof load stress: 175 ksi (up to 1")
- Hardness: 24 HRC min, 38 HRC max
- Suitable for: F3125 A325, F3125 A490 Type 1, F1554 Grade 105, A354 BD
Grade DH3 (heavy hex, weathering)
- Proof load stress: 175 ksi
- Hardness: 24 HRC min, 38 HRC max
- Material: Weathering steel matching A325 Type 3 / A490 Type 3 chemistry
- Suitable for: F3125 Type 3 (weathering) bolts
The DH vs 2H substitution
F3125 explicitly permits A194 Grade 2H heavy hex nuts as a substitute for A563 DH on Type 1 A325, A490, F1852, and F2280 bolts. The same allowance exists in metric (A194 2H for A563M 10S on A325M, A490M Type 1).
When 2H nuts are substituted:
- All A563 requirements still apply — including overtap amounts for coatings, coating grade, lubrication, and proof-load testing
- The advantage is supply availability and dual-purpose stocking; 2H nuts already in inventory for A193 stud work can cover structural bolt orders
- 2H cannot substitute for DH3 — weathering-steel structural service still requires DH3
Overtapping for galvanizing
When nuts are hot-dip galvanized or zinc-coated, threads are overtapped to accommodate coating buildup on the bolt. Required overtap amounts are specified in F2329 (HDG) and F1941 (zinc electroplating).
Critical: coated nuts must be proof-load tested after overtapping. Overtapping slightly reduces effective thread engagement, and proof-load testing confirms the nut-bolt assembly still develops full bolt tension before nut stripping.
Nut stripping vs bolt failure
A properly-spec'd structural connection fails the bolt in tension, not the nut in thread stripping. Heavy hex geometry plus the specified proof load stress ensures the nut is stronger than the bolt. Standard hex nuts (thinner pattern) do not provide this margin and must not be used in structural applications where F3125 or comparable strength classes are specified.
Marking
- Grade markings appear on one face of the nut
- Grade A: no mark required (but optional)
- Grades B, C, D, DH, DH3: grade letter(s) required
- Type 3 / weathering grades add an underline or "3" designator
- Manufacturer's identification symbol required
Applications
- Structural steel connections (F3125 pairing)
- Anchor bolt terminations (F1554 pairing)
- General mechanical assembly (A307 pairing)
- Bridge fabrication (DH3 for weathering-steel members)
- Equipment foundations and base plates
Related specifications
- F3125 — Structural bolts (primary pairing)
- F1554 — Anchor bolts
- A307 — General-purpose bolts
- A449 — Q&T bolts
- A354 — Alloy Q&T bolts (BC and BD grades)
- A194 — High-temp/pressure nuts (2H may substitute for DH on Type 1 structural bolts)
- F594 — Stainless steel nuts
- F2329 — HDG coating standard with nut overtap requirements
- F1941 — Zinc electroplating with nut overtap requirements
Documentation
California Fastener A563 orders ship with mill certificates showing grade, heat number, proof load test results, hardness, and coating thickness reports.