ASTM A563 Heavy Hex Nut Grades
ASTM A563 is the standard for carbon and alloy steel nuts — grade, proof load and hardness. Grades O, A and B for general service; C, C3, D, DH and DH3 for structural work, with proof-load stress from 69 to 175 ksi and the weathering-steel C3/DH3 variants.
Last updated: 2026-11
Specifications
ASTM A563 is the standard under which a steel nut's grade, proof load, coating and bolt compatibility are confirmed — the material-side half of a heavy hex nut specification. The grade ladder runs from Grade O (69 ksi proof-load stress, general light service) through A and B, into the structural grades: C and C3 (144 ksi), D (150 ksi) and the high-strength DH and DH3 (175 ksi, quenched and tempered), where C3 and DH3 are the atmospheric-corrosion-resistant (weathering) variants. General grades O, A and B cover 1/4"–1-1/2"; the structural grades run 1/4"–4". Grades O, A and B are also the only ones that need not carry a manufacturer identification mark alongside the grade marking. For structural bolting the choice is not free: A325 Type 1 bolts accept A563 C, C3, D, DH, DH3 and A194 2H nuts; A490 Type 1 accepts DH, DH3 or 2H; and the weathering A325 Type 3 / A490 Type 3 bolts pair with C3 and DH3 respectively. Hot-dip galvanized A325 needs DH or A194 2H.
| Standard | ASTM A563 — carbon and alloy steel nuts; the standard under which grade, proof load, coating and bolt compatibility are confirmed |
|---|---|
| Grade O | Carbon steel, 1/4"–1-1/2"; proof-load stress 69 ksi; hardness B55–C32 Rockwell |
| Grade A | Carbon steel, 1/4"–1-1/2"; proof-load stress 90 ksi; hardness B68–C32 Rockwell |
| Grade B | Carbon steel, 1/4"–1-1/2" (120 ksi through 1", 105 ksi over 1"); hardness B69–C32 Rockwell |
| Grade C / C3 | 144 ksi proof-load stress, 1/4"–4", B78–C38 Rockwell; C3 is the atmospheric-corrosion-resistant variant; may be quenched and tempered |
| Grade D | Carbon steel, 1/4"–4"; proof-load stress 150 ksi; hardness B84–C38 Rockwell |
| Grade DH / DH3 | 175 ksi proof-load stress, quenched and tempered, 1/4"–4", C24–C38 Rockwell; DH3 is the weathering variant |
| Structural pairing | A325 Type 1: A563 C/C3/D/DH/DH3 or A194 2H; A490 Type 1: DH/DH3/2H; A325 Type 3 & A490 Type 3: C3/DH3; galvanized A325: DH or 2H |
| Marking | Grades O, A and B need no manufacturer identification mark; all other grades must carry one beside the grade mark |
Materials
- Carbon steel
- Atmospheric-corrosion-resistant (weathering) steel
- Quenched and tempered carbon steel
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ASTM A563 Heavy Hex Nut Grades) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
Which A563 grade matches my A325 or A490 bolt?
Follow the compatibility chart, not just the strength numbers. A325 Type 1 accepts A563 grades C, C3, D, DH and DH3, plus A194 Grade 2H. A490 Type 1, the higher-strength bolt, narrows the field to DH, DH3 or 2H. Weathering-steel bolts lock the choice further: A325 Type 3 and A490 Type 3 pair with the atmospheric-corrosion-resistant grades C3 and DH3 (A490 Type 3 with DH3 only). And a hot-dip galvanized A325 takes DH or 2H. When in doubt, name the bolt specification and let the chart settle the nut grade — mixing a weathering bolt with a non-weathering nut creates the corrosion path the pairing rules exist to prevent.
What does the proof-load stress number on a nut grade mean?
It is the tabulated proof-load stress for the nut grade — the stress level the nut must sustain in the standardized proof-load test without measurable permanent deformation. It is a material-qualification figure, not a rating for a specific joint: the usable clamp load in an assembly depends on the nut size, thread series and the test geometry behind the grade. Use the grade ladder comparatively — O below A below B below C/D below DH — and pair grades to bolts by the compatibility rules rather than by trying to match ksi figures bolt-to-nut.
What is the MOQ and lead time for this nut type?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Common diameters in this nut type are widely stocked; confirm the exact schedule against quantity and size mix at quotation.
What should an RFQ for this nut type state?
State the standard designation (ASME B18.2.2 heavy hex, with the ASTM A563 or A194 grade called out), nominal thread size and threads-per-inch series, material and finish (plain, zinc-plated, or hot-dip galvanized where compatible), any required certificates such as a mill test report per EN 10204 3.1, and quantity per size — plus destination country.
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support