ASTM A563M Metric Nuts (Classes 5, 8, 8S, 10, 10S, 12) | Specifications

Standard Overview

What Is ASTM A563M?

The metric standard specification for carbon and alloy steel nuts paired with metric structural bolts, anchor studs, and engineering assemblies.

ASTM A563M is the metric companion standard to ASTM A563. It covers mechanical and chemical requirements for metric carbon and alloy steel nuts ranging from M6 to M100. Designed primarily to mate with metric high-strength structural bolts (such as ASTM F3125M Grade A325M and A490M, ISO 898-1 property classes 8.8 and 10.9), it defines two major nut geometry profiles:

Standard Metric Hex

ASTM A563M Hex (Style 1 & 2)

Standard metric hex profile for general structural connections, anchor studs, and machinery housings. Offered in Property Classes 5, 8, 10, and 12.

Profile: ASME B18.2.4.1M / ISO 4032 | Thread: Metric Coarse Pitch

Metric Heavy Hex

ASTM A563M Heavy Hex

Wider cross-section and increased height for maximum load dispersion. Mandatory for metric high-tensile structural bolts (A325M & A490M). Offered in Classes 8S, 10S, and 12S.

Profile: ASME B18.2.4.6M | Property Classes: 8S, 10S, 12S

                        Structural Pairing Guidance: High-strength metric structural bolts conforming to ASTM F3125M Grade A325M require ASTM A563M Class 8S or 10S Heavy Hex Nuts. Ultra-high tensile Grade A490M bolts mandate ASTM A563M Class 10S Heavy Hex Nuts to withstand extreme preloads.
                    

Technical Specifications

A563M Property Classes, Mechanical Properties & Coatings

Property Class Characteristics

Property Class 5: Non-heat-treated carbon steel nut designed for low-strength metric bolts (Class 4.6 / ASTM A307M).
Property Class 8: Carbon steel hex nut providing proof load capacity suitable for Class 8.8 metric fasteners.
Property Class 8S: High-strength carbon steel heavy hex nut specifically designed for ASTM F3125M Grade A325M structural bolts.
Property Class 10: Medium carbon quenched and tempered metric hex nut suitable for Property Class 10.9 general bolts.
Property Class 10S: Quenched and tempered alloy or medium carbon heavy hex nut engineered for maximum load carrying with A490M metric structural bolts.
Property Class 12 / 12S: Ultimate strength quenched and tempered alloy steel nut designed for Class 12.9 high-tensile bolting systems.

Proof Load Stress & Hardness Limits

Property Class	Nut Style	Size Range (mm)	Proof Load Stress (Uncoated)	Hardness Range (Rockwell / HV)
Class 5	Hex (Style 1)	M6 to M36	610 MPa	89 HRB max (180 HV)
Class 8	Hex (Style 1 / 2)	M6 to M36	920 MPa	89 HRB to C30
Class 8S	Heavy Hex	M12 to M36	1075 MPa	C24 to C32
Class 10	Hex (Style 1 / 2)	M6 to M36	1040 MPa	C26 to C36
Class 10S	Heavy Hex	M12 to M36	1245 MPa	C26 to C38
Class 12	Hex / Heavy Hex	M6 to M36	1200 MPa / 1330 MPa	C31 to C38

Hot-dip galvanized ASTM A563M nuts require special thread overtapping (indicated by tolerance position AZ or AX) to account for the zinc coating buildup while maintaining proof load capability.

Chemical Composition Limits

Property Class	Carbon (C)	Manganese (Mn)	Phosphorus (P)	Sulfur (S)	Material Type
Class 5	0.55% max	—	0.11% max	0.15% max	Low Carbon Steel
Class 8	0.55% max	0.30% min	0.060% max	0.15% max	Medium Carbon Steel
Class 8S	0.55% max	0.30% min	0.048% max	0.058% max	Medium Carbon Steel
Class 10S	0.20 – 0.55%	0.60% min	0.040% max	0.050% max	Medium Carbon / Alloy Steel
Class 12S	0.28 – 0.50%	0.45% min	0.035% max	0.035% max	Alloy Steel (Cr/Mo/V)

Dimension Tables

ASME B18.2.4.6M Metric Heavy Hex Nut Dimensions

Standard metric dimensions in millimetres (mm) for ASTM A563M heavy hex structural nuts.

Metric Heavy Hex Nut Dimensions (ASME B18.2.4.6M)

Nominal Size (D)	Thread Pitch (P)	Width Across Flats s (max)	Width Across Corners e (min)	Nut Thickness m (max)
M12	1.75 mm	21.00 mm	23.18 mm	12.30 mm
M16	2.00 mm	27.00 mm	29.56 mm	17.10 mm
M20	2.50 mm	34.00 mm	37.29 mm	20.70 mm
M22	2.50 mm	36.00 mm	39.55 mm	23.60 mm
M24	3.00 mm	41.00 mm	45.20 mm	24.20 mm
M27	3.00 mm	46.00 mm	50.85 mm	27.60 mm
M30	3.50 mm	50.00 mm	55.37 mm	30.70 mm
M36	4.00 mm	60.00 mm	66.44 mm	36.60 mm

                    Galvanized Overtapping Note: Metric hot-dip galvanized ASTM A563M nuts are overtapped (typically +0.35 mm to +0.53 mm depending on thread pitch) post-galvanizing in accordance with ASTM A563M Table 6 to ensure free assembly over zinc-coated male bolt threads.
                

Application Guidance

Where & How to Specify ASTM A563M Nuts

Metric Structural Steelwork

Class 8S and 10S heavy hex nuts are mandatory for connecting primary steel frame joints designed to metric ASTM F3125M (A325M / A490M) standards.

Railway & Rail Infrastructure

Specified for railway track fastenings, steel bridges, and overhead catenary structures where metric high-tensile fatigue resistance is critical.

Heavy Equipment & Mining

Used on heavy earthmoving gear, crusher plants, and structural frames requiring metric high proof-load fastenings under high vibration.

Metric Foundation Bolts

Class 8 and 10 nuts are widely used on metric foundation anchor rods for industrial plants, power stations, and turbine bases in the GCC.

Oil & Gas Process Modules

Class 10S nuts maintain tight clamping force on structural skids, offshore platforms, and heavy processing vessels in harsh environments.

Complete RFQ Format

"ASTM A563M Class 10S Heavy Hex Nut, M24 x 3.0, Hot-Dip Galvanized (ASTM F2329), with EN 10204 3.1 Mill Test Report."

Related Standards

Complementary Structural Standards

Standard	Description	Relationship to ASTM A563M
ASTM F3125M	Metric high-strength structural bolts (A325M/A490M)	Direct mating metric structural bolt standard requiring A563M nuts
ISO 4032 / 4033	Metric hexagon standard / high nuts	Alternative ISO metric nut standards for industrial machinery
ASTM F436M	Hardened metric steel washers	Companion metric structural washer placed under A563M nuts
ASME B18.2.4.6M	Metric heavy hex nuts dimensional standard	Governs dimensional geometry for A563M heavy hex nuts
ASTM A194M	Metric carbon and alloy steel nuts for high-pressure/temp	Alternative high-strength metric nut specification (e.g. Grade 2HM)
ASTM F2329 / F2329M	Hot-dip galvanizing for metric fasteners	Coating specification for zinc-galvanized A563M nuts

FAQ

Frequently Asked Questions

What is the difference between ASTM A563 and ASTM A563M?

ASTM A563 covers inch-series (imperial) carbon and alloy steel nuts, whereas ASTM A563M is the metric equivalent specification defining Property Classes (5, 8, 8S, 10, 10S, 12) with dimensions in millimetres.

Which A563M nut grade is required for A325M bolts?

For plain and galvanized metric A325M structural bolts, ASTM A563M Class 8S or Class 10S heavy hex nuts are required by structural design codes (such as AISC and Eurocodes).

Can an ISO 4032 Property Class 10 nut replace an A563M Class 10S nut?

Not directly in structural steel joints. ISO 4032 defines standard hex nut dimensions, whereas A563M Class 10S mandates heavy hex dimensions (ASME B18.2.4.6M) with a larger width across flats to distribute high structural preloads safely.

Why do galvanized A563M nuts need overtapping?

Hot-dip galvanizing adds a protective zinc layer typically 40–50 microns thick on the threads. Overtapping internal threads post-galvanizing enables the nut to spin freely onto the galvanized bolt without binding, while preserving structural strength.

Need ASTM A563M Metric Nuts in UAE & GCC?

We supply ASTM A563M Metric Heavy Hex Nuts in Classes 8S, 10S, and 12S from M12 to M64. Available finishes include Plain, Hot-Dip Galvanized (HDG), Zinc Plated, and PTFE. Complete stock with 3.1 Mill Test Reports dispatched from RAK FREEZONE.

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ASTM A563M Metric Carbon & Alloy Steel Nuts