ASTM A325 is an ASTM International

ASTM International

ASTM International, known until 2001 as the 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, and services...

 standard for heavy hex structural bolts

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from to 1- 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

ASTM International

ASTM International, known until 2001 as the 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, and services...

, 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
  Boron
  Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
  
   steel, or medium carbon alloy steel
• Type 2: Low carbon martensitic steel (withdrawn from the standard in 1991)
• Type 3: Weathering steel

Note that independent of the material the bolt is quench

Quench

In materials science, quenching is the rapid cooling of a workpiece to obtain certain material properties. It prevents low-temperature processes, such as phase transformations, from occurring by only providing a narrow window of time in which the reaction is both thermodynamically favorable and...

ed and temper

Temper

Temperare is the Latin origin of words like "temperature" and "tempering"; it and "tempo" come, in turn, from tempus...

ed.

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

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

Tensile strength

Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

. These bolts use the same material as their common cousins (ASTM F568M

ASTM F568M

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

 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.

For a higher strength version of this type of bolt, see ASTM A490

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 Tensile Strength, while the metric standard is titled...

.

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]
or	Type 1	–1 (inc.)	85	92	120	C24–35
		1–1-	74	81	105	C19–31
	Type 2	–1	85	92	120	C24–35
	Type 3	–1	85	92	120	C24–35
		1–1-	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]
	Type 1	12–36	600	660	830	C23–34
	Type 2
	Type 3