According to ASTM standards, A563 DH and ASTM A194 Grade 2H nuts are similar in terms of performance and sizes. Both nut types are heat-treated, high-strength heavy hex nuts commonly used in structural and industrial applications, and both of them are applicable to ASTM A325 and ASTM F1554 Grade 105 structural bolts. They share comparable mechanical properties, including tensile strength, hardness, and load-bearing capacity, making them interchangeable in many high-pressure, high-temperature, and heavy-duty settings. While their specifications differ in material composition, their performance characteristics, such as durability and size availability, align closely for use in demanding bolted assemblies.

ASTM A194 Grade 2H is a specification for high-strength heavy hex nuts made from carbon and alloy steel. These nuts are heat-treated to enhance strength and are used in high-pressure, high-temperature, and heavy-duty structural applications, such as pipelines, pressure vessels, and structural bolting assemblies.

Key Properties and Features:

1. Material Composition:

   • Medium carbon steel, heat-treated (quenched and tempered).

2. Heat Treatment:

   • Quenching and tempering to improve hardness, tensile strength, and toughness.

3. Mechanical Properties:

   • High tensile strength, capable of withstanding significant loads without deformation.
   • Increased hardness for durability in severe applications.

4. Application:

   • Used in high-temperature, high-pressure systems such as valves, flanges, and pressure vessels, as well as structural bolting assemblies in bridges, industrial machinery, and critical infrastructure.

5. Size Range:

   • Commonly produced in sizes ranging from 1/4 inch to 4 inches in diameter.

6. Corrosion Resistance:

   • Can be coated (e.g., zinc-plated or galvanized) to improve corrosion resistance in harsh environments.

7. Testing and Standards:

   • Must undergo proof load tests, hardness tests, and chemical analysis to verify compliance with ASTM standards.

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Technical Specifications of ASTM A194 Grade 2H:

Property	Specification
Material	Medium carbon steel (heat-treated)
Heat Treatment	Quenched and tempered
Tensile Strength	~1,000 MPa (145 ksi)
Proof Load	150,000 to 175,000 psi
Hardness	Rockwell C 24 – 35
Size Range	1/4 inch to 4 inches (heavy hex)
Shape	Heavy hex (for better load distribution and torque application)
Application	High-pressure, high-temperature, structural bolting
Corrosion Resistance	Requires coatings (e.g., zinc plating or galvanization)
Standards	ASTM A194 testing for proof load, hardness, and chemical analysis

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Applications:

• Structural Bolting: Commonly paired with ASTM A325 and A490 bolts for structural steel connections.
• High-Pressure Systems: Used in piping, flanges, valves, and pressure vessels.
• Heavy-Duty Machinery: Ensures secure and reliable connections in industrial machinery and equipment.