Grade A Heavy Hex Nuts: Specifications, Uses & Standards

Heavy Hex Nut vs. Standard Hex Nut

While both heavy hex nuts and standard (finished) hex nuts serve the same basic function, there are important differences in size, strength distribution, and typical use cases.

Key Differences

Heavy Hex Nuts

• Larger width across flats

• Greater thickness

• Increased bearing surface area

• Better load distribution under clamping force

• Commonly used in structural and industrial applications

Standard Hex Nuts

• Smaller width across flats

• Thinner profile

• Reduced bearing surface

• Intended for general-purpose, non-structural fastening

Why Heavy Hex Nuts Are Used

The increased size of a heavy hex nut allows clamping forces to be spread over a wider area. This reduces the risk of embedment into connected materials and improves joint stability, particularly in steel-to-steel connections and anchor rod assemblies.

Because of these characteristics, heavy hex nuts are preferred in applications where:

• Load distribution is critical

• Structural integrity is required

• Larger bearing surfaces improve joint performance

Compatible Bolt & Anchor Rod Grades

ASTM A563 Grade A Heavy Hex Nuts are intended for use with low-strength fasteners.

Compatible Fasteners

• ASTM A307

• ASTM A36

• ASTM F1554 Grade 36

• SAE Grade 2

Incompatible Fasteners

• ASTM A325

• ASTM A490

• Other high-strength structural bolts

Using Grade A nuts with high-strength bolts may result in improper joint performance and does not meet structural bolting requirements.

Finish & Coating Options

Grade A Heavy Hex Nuts are available in a variety of finishes to meet corrosion resistance and environmental requirements:

• Plain (as-manufactured)

• Hot-dip galvanized

• Zinc plated

• Mechanical galvanized

• Specialty coatings (availability varies)

Galvanizing Considerations

Hot-dip galvanized Grade A heavy hex nuts are tapped oversize in accordance with ASTM A563 to compensate for coating thickness and ensure proper thread fit.

Mechanical Properties

1. To determine nut proof load in pounds, multiply the appropriate nut proof load stress by the tensile stress area of the thread.
2. Non-zinc-coated nuts are nuts intended for use with externally threaded fasteners which have a plain (nonplated or noncoated) finish or have a plating or coating of insufficient thickness to necessitate overtapping the nut thread to provide assemblability. Zinc-coated nuts are nuts intended for use with externally threaded fasteners which are hot-dip zinc-coated, mechanically zinc-coated, or have a plating or coating of sufficient thickness to necessitate overtapping the nut thread to provide assemblability.

Chemical Properties

1. For Grade A a sulfur content of 0.23 % max is acceptable with the purchasers approval.