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.
Contents
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.
In 2016, specifications A325 and A490 were officially withdrawn by ASTM and replaced by ASTM F3125. A325 and A490 heavy hex structural bolts are now grades under the new F3125 specification.
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:
Note that independent of the material the bolt is quenched and tempered.
Connection types
There are also three connection types defined:
Mechanical properties, imperial
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 yield 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.
For a higher strength version of this type of bolt, see ASTM A490.