Structural Hex Nuts
What Are Structural Hex Nuts?
Structural hex nuts (often called heavy hex nuts) are high-strength, large-profile hexagonal nuts engineered to clamp structural members with structural bolts in steel construction. Compared with standard hex finish nuts, structural nuts have a larger across-flat size and thicker height to deliver higher bearing area and strength.
Key Benefits of Structural Hex Nuts
- High strength: Manufactured to structural grades (e.g., A563 Grade A, C, DH, or DH3; ASTM A194 for alloy/stainless) to pair with structural bolts.
- Greater clamping area: Larger across-flats and thickness provide higher bearing and improved joint integrity.
- Corrosion protection options: Hot-dip galvanized and zinc-plated carbon steel for outdoor or sheltered use; stainless or silicon bronze for corrosive environments.
- Standards compliance: Produced to common inch and metric specifications for consistent fit with structural fasteners and erection practices.
Common Applications
- Steel buildings, bridges, and highway structures
- Industrial platforms, mezzanines, and crane runway systems
- Wind turbines, heavy equipment frames, and infrastructure
- Any critical bolted connection where high preload and reliability are required
Materials & Finishes
- Carbon/alloy steel: A563 Grades A/C (standard), DH/DH3 (high strength); available plain, zinc-plated, or hot-dip galvanized.
- Stainless steel: For corrosion resistance in outdoor/marine environments; pair with stainless structural bolts where specified.
- Silicon bronze: Non-sparking and corrosion-resistant for specialty environments.
Sizing & Standards
Available in inch sizes (e.g., 1/2"–13 through 1-1/2"–6 and larger) and metric sizes. Select nuts to match the bolt’s diameter and thread pitch. Typical governing specs include ASTM A563 (nut strength and marking), ASTM A153/A123 (hot-dip galvanizing), and project-specific standards or RCSC/AISC guidelines for structural bolting.
Installation Guidelines
- Verify nut grade and finish match the structural bolt and project specification.
- Tighten per the project’s approved method (turn-of-nut, calibrated wrench, or DTI) without backing off to align.
- For galvanized sets, use compatible, properly lubricated hardware; follow slip-coating requirements if applicable.
- Always replace any nut that shows thread damage, galling, or deformation.
Inspection & Maintenance
- Confirm grade markings and finish before assembly.
- Check final rotation/torque or DTI compression per the specified method.
- Re-inspect after initial loading or as required by site QA/QC procedures.
Structural Hex Nuts — FAQs
A structural hex nut (heavy hex nut) is a high-strength, large-profile hex nut used with structural bolts to clamp steel members in critical connections. It has a larger across-flats size and thickness than a standard hex nut for higher bearing area and clamping force.
Structural hex nuts are thicker and wider, made to higher strength grades, and intended for structural bolting methods (turn-of-nut, calibrated wrench, or DTI). Standard hex finish nuts are general-purpose and lower profile.
ASTM A563 Grades A/C (standard strength) and Grades DH/DH3 (high strength) are common. Stainless and silicon bronze options are used where corrosion resistance or specialty properties are required.
Yes. Use hot-dip galvanized carbon steel for most outdoor exposure. In highly corrosive or marine settings, 316 stainless steel or silicon bronze is recommended.
Match the nut to the bolt’s nominal diameter and thread pitch (e.g., 3/4-10, 7/8-9, or metric). Verify compatibility with the project specification and the bolt’s coating/finish.
Follow the specified method on the drawings (turn-of-nut, calibrated wrench, or DTI). Do not back off after final tightening to align holes. For galvanized sets, use compatible lubricants and washers as specified and replace any nut that shows galling or thread damage.
Confirm grade markings and finish before assembly, verify final rotation/torque or DTI compression after tightening, and re-inspect per QA/QC procedures or after initial loading if required.