ASTM A563 Nuts (Grade A, B, C, DH, DH3) | Specifications

Standard Overview

What Is ASTM A563?

The standard specification for carbon and alloy steel nuts designed for high-strength structural bolting, piping, and general steel fabrication.

ASTM A563 (and its metric equivalent ASTM A563M) covers chemical and mechanical requirements for carbon and alloy steel nuts ranging from 1/4" to 4" (M6 to M100) in diameter. These nuts are designed to mate perfectly with structural bolts like ASTM A307, ASTM A325, ASTM A490, ASTM A354, and ASTM F3125.

Standard Hex Nuts

ASTM A563 Finished Hex

Standard hex profile for general construction, low-to-medium strength bolting (ASTM A307), and non-critical machinery. Available in Grade A and Grade B.

Profile: ASME B18.2.2 Hex | Thread: UNC, UNF, or 8UN

Heavy Hex Nuts

ASTM A563 Heavy Hex

Thicker wall and wider cross-section for maximum thread engagement and load distribution. Mandatory for high-tensile structural bolts (ASTM A325 / A490).

Profile: ASME B18.2.2 Heavy Hex | Grades: C, DH, DH3

                        Structural Pairing Requirement: High-tensile structural bolts like ASTM F3125 Grade A325 require ASTM A563 Grade C or DH Heavy Hex Nuts. Ultra-high-strength Grade A490 bolts mandate ASTM A563 Grade DH or DH3 Heavy Hex Nuts to prevent thread stripping under extreme preloads.
                    

Technical Specifications

A563 Grades, Heat Treatment & Coatings

Grade Overview & Characteristics

Grade A: Carbon steel nut designed for general application with low-strength bolts (ASTM A307 / Grade 2). Available in hex or heavy hex style.
Grade B: Medium carbon steel nut providing higher proof load strength than Grade A. Suitable for Grade 5 / ASTM A449 bolting.
Grade C: Carbon steel heavy hex nut, typically furnished stress-relieved or quenched and tempered for high-load structural steel joints.
Grade DH: Quenched and tempered medium carbon or alloy steel heavy hex nut delivering extreme proof load resistance for ASTM A490 / Grade 8 structural systems.
Grade DH3: Weathering steel alloy heavy hex nut offering atmospheric corrosion resistance matching ASTM F3125 Type 3 / A588 weathering steel.

Proof Load & Hardness Requirements

Nut Grade	Nut Style	Size Range (Inches)	Proof Load Stress (Uncoated)	Hardness Range (Rockwell)
Grade A	Hex / Heavy Hex	1/4" to 1-1/2"	90,000 psi (Hex) / 100,000 psi (Heavy)	B68 – C32 (95 HRB max)
Grade B	Hex / Heavy Hex	1/4" to 1-1/2"	120,000 psi (Hex) / 133,000 psi (Heavy)	B69 – C32
Grade C	Heavy Hex	1/4" to 4"	144,000 psi	B78 – C38
Grade DH	Heavy Hex	1/4" to 4"	175,000 psi	C24 – C38
Grade DH3	Heavy Hex (Weathering)	1/4" to 4"	175,000 psi	C24 – C38

Hot-dip galvanizing reduces proof load capabilities slightly; therefore, ASTM A563 mandates overtapping of galvanized nuts per ASTM A563 Table X1.1 to accommodate zinc coating thickness.

Chemical Composition Limits

Grade	Carbon (C)	Manganese (Mn)	Phosphorus (P)	Sulfur (S)	Alloy Elements
Grade A	0.55% max	—	0.12% max	0.15% max	Carbon Steel
Grade B	0.55% max	—	0.12% max	0.15% max	Carbon Steel
Grade C	0.55% max	0.30% min	0.048% max	0.058% max	Carbon Steel
Grade DH	0.20 – 0.55%	0.60% min	0.040% max	0.050% max	Medium Carbon / Alloy Steel
Grade DH3	0.20 – 0.53%	0.40% min	0.040% max	0.040% max	Cr, Ni, Cu (Weathering)

Dimension Tables

ASME B18.2.2 Heavy Hex Nut Dimensions

Standard imperial dimensions in inches for ASTM A563 heavy hex structural nuts.

Imperial Heavy Hex Nut Dimensional Specs

Nominal Size (D)	Threads Per Inch (UNC)	Width Across Flats F (Basic)	Width Across Corners C (min)	Thickness H (Basic)
1/2"	13 TPI	7/8" (0.875)	0.969"	31/64" (0.484)
5/8"	11 TPI	1-1/16" (1.062)	1.175"	39/64" (0.609)
3/4"	10 TPI	1-1/4" (1.250)	1.383"	47/64" (0.734)
7/8"	9 TPI	1-7/16" (1.438)	1.589"	55/64" (0.859)
1"	8 TPI	1-5/8" (1.625)	1.796"	63/64" (0.984)
1-1/8"	7 TPI / 8UN	1-13/16" (1.812)	2.002"	1-7/64" (1.109)
1-1/4"	7 TPI / 8UN	2" (2.000)	2.209"	1-7/32" (1.219)
1-3/8"	6 TPI / 8UN	2-3/16" (2.188)	2.416"	1-11/32" (1.344)
1-1/2"	6 TPI / 8UN	2-3/8" (2.375)	2.622"	1-29/32" (1.469)

                    Galvanized Overtapping Note: Hot-dip galvanized ASTM A563 nuts (A563 DH HDG) are overtapped up to 0.021" (depending on diameter) post-galvanizing to allow smooth assembly over zinc-coated bolt threads.
                

Application Guidance

Where & How to Specify ASTM A563 Nuts

Structural Steel Framing

A563 Grade DH heavy hex nuts are mandatory for connecting primary steel beams, trusses, and columns using ASTM F3125 structural bolt assemblies.

Bridges & Infrastructure

Grade DH3 weathering nuts are widely used on unpainted highway bridges, portal gantries, and exposed steel structures throughout the GCC.

Transmission Towers & Substations

Hot-dip galvanized A563 Grade C heavy hex nuts ensure long-term atmospheric corrosion resistance on power transmission monopoles.

Foundation Anchor Bolts

Used extensively as double top-nuts on heavy anchor bolt assemblies (ASTM F1554 Grade 36, 55, and 105) for industrial plants.

Oil & Gas Steel Skids

High-tensile Grade DH nuts maintain precise torque preloads under severe operational vibration in modular refinery processing skids.

Complete RFQ Format

"ASTM A563 Grade DH Heavy Hex Nut, 3/4"-10 UNC, Hot-Dip Galvanized (ASTM F2329), with EN 10204 3.1 MTR."

Related Standards

Complementary Structural Standards

Standard	Description	Relationship to ASTM A563
ASTM F3125	High-strength structural bolt specification (A325/A490)	Direct mating structural bolt specification requiring A563 nuts
ASTM A194 / A194M	Carbon and alloy steel nuts for high-pressure/temperature service	Alternative high-strength nut standard (e.g. Grade 2H) used in piping
ASTM F436 / F436M	Hardened steel washers	Companion structural washer placed under A563 nuts
ASTM F1554	Anchor bolts for structural foundations	Specifies A563 Grade A, C, or DH nuts for anchor assemblies
ASME B18.2.2	Square and hex nuts (Imperial)	Dimensional standard governing A563 nut geometry
ASTM F2329	Hot-dip galvanizing for threaded fasteners	Coating specification for zinc-galvanized A563 nuts

FAQ

Frequently Asked Questions

Can I substitute an ASTM A194 2H nut for an ASTM A563 Grade DH nut?

Yes, in most cases. ASTM A194 Grade 2H heavy hex nuts meet or exceed the proof load and hardness requirements of ASTM A563 Grade DH nuts and are widely accepted by structural engineering standards (AISC) as a direct alternative.

Which A563 nut grade is required for A325 structural bolts?

For plain (uncoated) A325 bolts, ASTM A563 Grade C or DH heavy hex nuts are required. For hot-dip galvanized A325 bolts, ASTM A563 Grade DH heavy hex nuts are mandatory to maintain proper load capacity after overtapping.

What is the difference between A563 and A563M?

ASTM A563 covers inch-series (imperial) nuts, whereas ASTM A563M covers metric-series nuts (Property Classes 8S, 10S, etc.). Both follow similar mechanical principles adapted to their respective unit systems.

Why are heavy hex nuts preferred over standard hex nuts in structural joints?

Heavy hex nuts have a larger width across flats and greater thread length. This increases thread shear area and bearing surface area, preventing thread stripping and reducing contact stress under severe structural preloads.

Need ASTM A563 Structural Nuts in UAE & GCC?

We stock ASTM A563 Heavy Hex Nuts in Grade A, C, DH, and DH3 from 1/2" to 4" diameter. Finishes include Plain, Hot-Dip Galvanized (HDG), Cadmium, and PTFE (Xylan). Fast supply with 3.1 MTR certification from RAK FREEZONE.

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ASTM A563 Carbon & Alloy Steel Nuts