Heavy hex nuts are hexagonal threaded fasteners manufactured to a larger across-flats dimension and increased thickness than standard finished hex nuts of the same nominal diameter. The heavy pattern is defined by applicable dimensional standards and is commonly specified in structural and high-load bolted assemblies.
- Description
- Specifications
Heavy hex nuts are used where bolt systems, joint design, or governing specifications require the heavy hex configuration rather than the finished hex series. Selection is driven by applicable standards and project documentation.
Dimensional Pattern
Heavy hex nuts follow dimensional requirements established by ASME B18.2.2 and related structural standards. For a given nominal diameter, the heavy hex pattern provides increased width across flats and greater thickness compared to the finished hex configuration.
This dimensional pattern aligns with structural bolt systems and certain pressure or high-temperature bolting applications where the governing specification calls for heavy hex geometry.
Structural Applications of Heavy Hex Nuts
In structural steel construction, heavy hex nuts are typically specified for use with structural bolts governed by ASTM F3125 (including Grades A325 and A490). In these assemblies, nut grade must correspond to bolt grade and preload requirements are defined by the applicable structural standard.
Heavy hex nuts in structural applications are commonly supplied to ASTM A563 grades appropriate to the bolt system and coating requirements.
Non-Structural and Pressure Applications
Heavy hex nuts are also specified outside structural steel construction. ASTM A194 (or A194M) covers carbon, alloy, and stainless steel nuts intended for high-pressure and high-temperature service. The A194 standard includes multiple grades suited to different materials and service conditions, including but not limited to Grades 2H, DH, B7, B8, and B8M.
These grades may be supplied in heavy hex or finished hex dimensional patterns depending on the governing specification. Detailed grade selection is determined by the applicable code, pressure vessel requirement, or customer drawing.
Use with Stud Bolts and Structural Washers
Heavy hex nuts are frequently used with fully threaded studs (stud bolts) in structural, flange, and pressure assemblies. In these applications, nuts are installed on both ends of the stud rather than on a headed bolt.
Where required by governing specifications, structural washers of the appropriate grade are used in conjunction with heavy hex nuts to distribute bearing load and protect connected materials. Nut grade, washer grade, and stud grade must align with the applicable ASTM or project specification.
How G-Fast Supports Structural, Industrial and Government Requirements
G-Fast supplies heavy hex nuts for structural, industrial, government applications in accordance with applicable ASTM and ASME specifications. We support both commercial and government-specified projects and work strictly from approved customer documentation.
To evaluate availability or submit a specification, request a quote through the website.
Hot-Dip Galvanized Configurations
In structural applications requiring hot-dip galvanizing (HDG), heavy hex nuts are typically tapped oversize to accommodate the coating thickness applied to galvanized bolts or studs. Proper fit between galvanized components is governed by applicable ASTM and ASME standards to ensure correct assembly and thread engagement.
Oversized tapping in galvanized assemblies is a function of coating thickness and is not considered a dimensional defect.
Materials and Finishes
Heavy hex nuts are available in a range of materials depending on application requirements, including carbon steel, alloy steel, stainless steel, bronze, and galvanized configurations for structural use.
Surface treatments and coatings are specified to align with bolt coating systems and environmental exposure conditions.