ASTM A325 is an

ASTM International ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, ...

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 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.. This is a standard set by the standards organization

, a voluntary standards development organizations that sets technical standards for materials, products, systems, and services. In 2016, ASTM officially withdrew specification A325 and replaced it with ASTM F3125. To minimize confusion, bolt head markings are unchanged and the designation A325 is retained as a grade name within the new standard. In 1951, A325 bolts were recognized as equivalent to a hot driven ASTM A141 rivet.

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 Boron steel refers to steel alloyed with a small amount of boron, usually less than 1%. The addition of boron to steel greatly increases the hardenability of the resulting alloy. Description Boron is added to steel as ferroboron (~12-24% B). As ...

, or medium carbon

alloy steel Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low alloy steels and high alloy steels. The differe ...

*Type 2: Low carbon

martensitic Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation. Properties Mart ...

steel. (withdrawn from the standard in 1991) *Type 3:

Weathering steel Weathering steel, often referred to by the genericised trademark COR-TEN steel and sometimes written without the hyphen as corten steel, is a group of steel alloys which were developed to eliminate the need for painting, and form a stable rus ...

There is also a ''T'' version, which is used to refer to fully threaded bolts. Note that independent of the material the bolt is

quench In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as phas ...

ed and tempered.

Connection types

There are also three connection types defined: *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

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 ASTM F568M is an ASTM International standard for metric bolts, screws and studs that are used in general engineering applications. It is titled: ''Standard Specification for Carbon and Alloy Steel Externally Threaded Metric Fasteners''. It defines ...

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. Nuts must meet ASTM A563, which also uses heavy hex geometry. Dimensions of heavy hex geometry are per document ANSI/ASME B18.2.6, which uses "coarse" threads as defined by

Unified Thread Standard The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a w ...

. ASTM 325 bolts can be considered equivalent to Grade 8.8 bolts according to

. For a higher strength version of this type of bolt, see

ASTM A490 ASTM A490 and ASTM A490M are ASTM International standards for heavy hex structural bolts made from alloy steel. The imperial standard is officially titled ''Standard Specification for Structural Bolts, Alloy Steel, Heat Treated, 150 ksi Minimum Te ...

Mechanical properties, metric

/mm

References