ASTM A325 Specifications

Technical Menu Posted on July 1st, 2015 by vapro

ASTM A325 is an ASTM International standard for heavy hex structural bolts, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from 1⁄2 to 1-1⁄2 in diameter. The equivalent metric standard is ASTM A325M, which is titled Standard Specification for Structural Bolts, Steel, Heat Treated 830 MPa Minimum Tensile Strength. It defines mechanical properties for sizes M12–36. There is also a T version, which is used to refer to fully threaded bolts. This is a standard set by the standards organization ASTM International, a voluntary standards development organizations that sets technical standards for materials, products, systems, and services.

Types

The “type” refers to the type of material used to make the bolt. The standard currently defines two types, however it previously defined the following three:

  • Type 1: Medium carbon steel, boron steel, or medium carbon alloy steel
  • Type 2: Withdrawn from the standard in 1991
  • Type 3: Weathering steel

Connection Types

  • SC: A slip critical connection.
  • N: A bearing type connection where the threads are on the shear plane.
  • X: A bearing type connection where the threads are not on the shear plane.

Mechanical Properties

These types of bolts are designed to be tightened to near their proof strength, in order to create significant bolt tension. The standard states that the bolts must be tightened to at least 70% of the tensile strength. These bolts use the same material as their common cousins (ASTM F568M for metric bolts), but have a thicker and wider head to more effectively distribute the load. This modified geometry is often referred to as heavy hex geometry. ASTM 325 bolts can be considered equivalent to Grade 8.8 bolts according to ASTM F568M.

Head markings and mechanical properties for imperial sizes
Head marking Grade Nominal size
range [in]
Proof strength [ksi] Yield strength
(min) [ksi]
Tensile strength
(min) [ksi]
Core hardness
[Rockwell]
A325 ASTM A325 Type 1 1⁄2–1 (inc.) 85 92 120 C24–35
1–1-1⁄2 74 81 105 C19–31
\ | / ASTM A325 Type 2 1⁄2–1 85 92 120 C24–35
A325 ASTM A325 Type 3 1⁄2–1 85 92 120 C24–35
1–1-1⁄2 74 81 105 C19–31
Head markings and mechanical properties for metric sizes
Head marking Grade Nominal size range [mm] Proof strength [MPa] Yield strength (min) [MPa] Tensile strength (min) [MPa] Core hardness [Rockwell]
A325M
8S
ASTM A325M Type 1 12–36 600 660 830 C23–34
A325M
8S
ASTM A325M Type 2
A325M
8S3
ASTM A325M Type 3

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