A Detailed Guide to ASTM A325 Structural Bolts

What Is an A325 Structural Bolt?

A325 structural bolts (ASTM A325 Heavy Hex Structural Bolts) are high-strength bolts primarily used to connect steel structural components. According to the American Society for Testing and Materials (ASTM) standards, A325 bolts are classified into three performance grades: Grade 1, Grade 2, and Grade 3. Type 1 bolts are made of boron steel or alloy steel; Type 2 has been discontinued; and Type 3 is manufactured from weathering steel and is primarily used for corrosion resistance in atmospheric environments.

A325 Bolt Types

Types	Notes
TYPE 1	Medium carbon, carbon boron, or medium carbon alloy steel. Hot-dip galvanizing is available.
TYPE 2	Withdrawn November 1991.
TYPE 3	Weathering steel. Its weather resistance and corrosion resistance are equivalent to those of A242, A556, and A709 steels, making it suitable for use with weathering steel.
T	Fully threaded A325.(Restricted to 4 times the diameter in length)
M	Metric A325.

Applications of A325 Bolts

A325 structural bolts are widely used in bridge construction, steel frame connections, and the assembly of components for photovoltaic, wind power, and solar energy systems. These bolts are not only used to secure the main structure but are also frequently employed to connect critical support points or load-bearing sections.

In bridge construction, bridges are subjected to complex loads, placing high demands on the strength and durability of the materials used. A325 bolts meet these requirements with their excellent performance, ensuring the structural stability and service life of bridges.

Features of A325 Structural Bolts

• High tensile strength (≥825 MPa)
• Suitable for structural connections
• Short thread length (enhances shear performance)
• Used in conjunction with high-strength nuts and washers

What is ASTM F3125?

The ASTM A325 standard has been officially withdrawn and replaced by ASTM F3125. A325 is now a specification. The F3125 specification consolidates and replaces six ASTM standards, including A2280. We have chosen to retain technical information regarding the now-obsolete A325 specification for informational purposes only. Prior to its withdrawal from the market in 2016, the ASTM A325 standard covered high-strength heavy-duty hexagonal structural bolts ranging from 1/2 inch to 1-1/2 inches in diameter. These bolts are intended for structural connections and therefore have a shorter thread length than standard hexagonal bolts; this standard applies exclusively to heavy-duty hexagonal structural bolts.

ASTM F3125 is a consolidated standard that combines several specifications for structural bolts, including:

• A325
• A490
• F1852
• F2280

A325 Bolt Specifications

Thread Specifications		1/2	5/8	3/4	7/8	1	1-1/8	1-1/4	1-3/8	1-1/2
d
ds	max	0.515	0.642	0.768	0.895	1.022	1.149	1.277	1.404	1.531
	min	0.482	0.605	0.729	0.852	0.976	1.098	1.223	1.345	1.47
s	Nominal	7/8	1-1/16	1-1/4	1-7/16	1-5/8	1-13/16	2	2-3/16	2-3/8
	max	0.875	1.062	1.25	1.438	1.625	1.812	2	2.188	2.375
	min	0.85	1.031	1.212	1.394	1.575	1.756	1.938	2.119	2.3
e	max	1.01	1.227	1.443	1.66	1.876	2.093	2.309	2.526	2.742
	min	0.969	1.175	1.383	1.589	1.796	2.002	2.209	2.416	2.622
k	Nominal	5/16	25/64	15/32	35/64	39/64	11/1616	25/32	27/32	15/16
	max	0.323	0.403	0.483	0.563	0.627	0.718	0.813	0.878	0.974
	min	0.302	0.378	0.455	0.531	0.591	0.658	0.749	0.81	0.902
b	reference	1	1.25	1.38	1.5	1.75	2	2	2.25	2.25
①,The chemical composition and mechanical properties shall conform to ASTM A 325 or ASTM A 490.

A325 Bolts Mechanical Properties

Nominal diameter (inches)	Tensile strength σb (MPa)	Yield strength σs (MPa)	Elongation at break (δ%)	Cross-sectional reduction ratio ψ%	Hardness HBW
1/2 ~ 1	≥825	≥635	≥14	≥35	253~319
＞1 ~ 1-1/2	≥725	≥560	≥14	≥35
1-1/8 ~ 1-1/2	≥725	≥560	≥14	≥35	223~286

A325 Type 3 Chemical Properties

Heat Analysis	120ksi, % Comp A	120ksi, % Comp B	120ksi, % Index	150ksi, % Index
Carbon	0.33 – 0.40	0.38 – 0.48	0.30 – 0.52	0.30 – 0.53
Manganese	0.90 – 1.20	0.70 – 0.90	0.60 min	0.60 min
Phosphorus	0.035 max	0.035 max	0.035 max	0.035 max
Sulfur	0.040 max	0.040 max	0.040 max	0.040 max
Silicon	0.15 – 0.30	0.30 – 0.50
Copper	0.25 – 0.45	0.20 – 0.40	0.20 – 0.60	0.20 – 0.60
Nickel	0.25 – 0.45	0.50 – 0.80	0.20 min*	0.20 min*
Chromium	0.45 – 0.65	0.50 – 0.80	0.20 min	0.20 min
Molybdenum		0.06 max	0.10 min*	0.10 min*
*Either Nickel or Molybdenum must be present in the amount specified *Corrosion Index based on ASTM Guide G101

ASTM A325 & A490 Bolt Clamping Force

Bolt Grade	Bolt Nominal Diameter mm，（inch）	Clamping Force (tf)
A325	16（5/8）	8.6
	19（3/4）	12.7
	22（7/8）	17.8
	25（1）	23.2
A490	16（5/8）	10.9
	19（3/4）	15.9
	22（7/8）	22.3
	25（1）	29.1
	28（1-1/8）	36.3
	32（1-1/4）	46.4
	35（1-3/8）	55.0
	38（1-1/2）	67.3

A325 Bolt Recommended Hardware

Nuts			Washers
Type 1		Type 3	Type 1	Type 3
Plain	Galvanized	Plain
A563C, C3, D, DH, DH3	A563DH	A563C3, DH3	F436-1	F436-3
Note: Nuts conforming to A194 Grade 2H are a suitable substitute for use with A325 heavy hex structural bolts. The ASTM A563 Nut Compatibility Chart has a complete list of specifications.