2H Heavy Hex Nuts: Technical Specifications and Material Data

Material and Chemical Composition

Mechanical Properties and Heat Treatment

Thread Specifications

• Thread Type: Typically produced in UNC (Unified National Coarse) or UNF (Unified National Fine) threads.

• Thread Series: For sizes 1" and larger, the 8 Thread Per Inch (8-UN) series is frequently specified, particularly for pressure vessel and flanging applications, to achieve better load distribution across the threads.

• Thread Class: Generally supplied in Class 2B thread fit (Inch series) or 6H (Metric series).

Equivalent Grades: ASTM A194 Grade 2H vs. ASTM A563 Grade DH

ASTM A194 Grade 2H nuts are often used as an acceptable equivalent to ASTM A563 Grade DH nuts in high-strength structural and pressure applications. Both grades share comparable mechanical properties, including similar proof load, hardness, and tensile strength requirements.

While Grade DH nuts are covered under ASTM A563 (typically used for structural bolting), Grade 2H nuts are specified under ASTM A194 for use in high-temperature and high-pressure service. Because their mechanical performance criteria overlap, ASTM A194 Grade 2H nuts are frequently substituted for Grade DH when approved by the project specification or engineer of record.

Head Markings

ASTM A194 Grade 2H Heavy Hex Nuts are required to have permanent markings stamped into one face to ensure traceability and verify material integrity for critical applications.

Grade Identification: The stamped "2H" indicates the nut meets all requirements of the ASTM A194 standard, including chemical composition, Quenched and Tempered heat treatment, and mechanical properties.

Manufacturer Identification: Each nut must also carry a unique trademark or registered symbol. This marking provides essential traceability, linking the fastener to its production lot and the associated Material Test Report (MTR).

These permanent markings are vital for quality assurance, on-site inspections, and confirming the correct high-strength fastener is used in high-pressure, high-temperature bolted connections.