Structural Carbon Steel Hex Bolt ASTM F3125 / F3125M

ASTM F3125/F3125M is a structural bolt specification covering inch and metric bolt grades. This specification contains 4 inch series bolting grades: A325, F1852, A490, and F2280. These will be addressed in this article. When looking at the mechanical requirements of bolts it appears that a grade A325 and SAE J429 Grade 5 are identical as do the grade A490 and the SAE J429 Grade 8.

This begs the question, "Can an SAE J429 Grade 5 be used when an ASTM F3125 grade A325 is specified?" The answer is definitely no. This is also the case for substituting a Grade 8 when grade A490 is specified, and here are some reasons why:

First, grade A325 and A490 bolts are produced with a heavy hex head configuration which provides a wider bearing surface over which to distribute the load. Grade 5 and 8 bolts are produced to standard hex cap screw configuration and therefore cannot distribute the load as much as is needed for structural applications.

Second, the shank length (non-threaded portion of the body) on the grade A325 and A490 bolts is designed to be greater (shorter thread lengths) than your standard hex bolt or hex cap screw. Remember, the weakest section of standard carbon steel fasteners is through the threaded region. Minute design changes such as this can create a stronger tensile connection.

Third, the difference in thread length is also likely to result in a change in shear strength. The following two diagrams demonstrate this difference:

Note: In 2016, ASTM A325 was officially withdrawn and replaced by ASTM F3125, in which A325 now becomes a grade under the F3125 specification. The F3125 specification is a consolidation and replacement of six ASTM standards, including; A325, A325M, A490, A490M, F1852, and F2280. We are choosing to keep this technical information about the now obsolete A325 specification on our website for reference and informational purposes only.

Prior to its withdrawl in 2016, the ASTM A325 specification covered high strength heavy hex structural bolts from 1/2″ diameter through 1-1/2″ diameter. These bolts are intended for use in structural connections and therefore have shorter thread lengths than standard hex bolts. Refer to the Structural Bolts page of our site for thread lengths and other related dimensions.

This specification is applicable to heavy hex structural bolts only. For bolts of other configurations and thread lengths with similar mechanical properties, see Specification A449.

Bolts for general applications, including anchor bolts, are covered by Specification A449. Also refer to Specification A449 for quenched and tempered steel bolts and studs with diameters greater than 1-1/2″ but with similar mechanical properties.

Mechanical Properties of ASTM F3125/F3125M Grades A325 & A490 Structural Bolts with Nut Compatibility

Grade A325 bolts are available in diameters from 1/2 to 1-1/2 inch (for diameters greater than 1-1/2, ASTM A449 specifications should be considered) with a minimum tensile strength of 120,000 PSI. They also come in two types. Type 1 is a medium carbon steel and can be galvanized; Type 3 is a weathering steel that offers atmospheric corrosion resistance similar to that of ASTM A242 or A588 steels. Type 3 grade A325 bolts shall be marked "A325" to distinguish them from standard grade A325s.

Grade A490 bolts are available in diameters from 1/2 to 1-1/2 inch diameters with a minimum tensile strength of 150,000 PSI for all diameters, and are offered in two types. Type 1 is alloy steel, and Type 3 is weathering steel that offers atmospheric corrosion resistance similar to that of ASTM A242 or A588 steels. Type 3 grade A490 bolts shall be marked "A490".

ASTM A490 bolts should not be galvanized or electroplated. The problem with hot dip galvanizing is that the molten bath of zinc exceeds the fastener's tempering temperature and would cause the fastener to anneal in the bath. In addition, a major problem with hot dip galvanizing and electroplating grade A490 bolts is the potential for hydrogen embrittlement. This scenario may occur when atomic hydrogen is introduced during the pickling process that takes place prior the plating or hot dip galvanizing process.

Process flow

Cold forging

Annealing treatment(if need) ➨ wiredrawing ➨ clod forging ➨ thread rolling ➨make heat treatment ➨ Finish ➨ Packing

Hot forging

Cutting material ➨ hot forging ➨ turning ➨ shrink diameter(half thread) ➨thread rolling ➨ make heat treatment ➨ Finish ➨ Packing

Materials and Chemical compstition

1035

1045

40CR

Finish

PLAIN ZP YZP BLACK HDG DACROMET GEOMET CHROME NICKEL AND SO ON

PACKING

QBH BULK

20-25KG/CTN,36CTNS/PALLET

20-30KG/BAGS,36BAGS/PALLET

ONE TON/BOXES

50KG/ IRON DRUM,12 IRON DRUMS/PALLET

QBH SMALL PACKING

Packing in small boxes according to customer’s requirements

Packing in plastic bag according to customer’s requirements

QBH PALLET TYPE

SOLID WOOD FUMIGATION PALLET

EURO Pallet

THREE SPLINT PALLET

WOODEN BOX

General:

In brief Type 3 grade A325 bolts shall be marked “A325” to distinguish them from standard grade A325s. Likewise Grade A490 bolts are available in diameters from 1/2 to 1-1/2 inch diameters with a minimum tensile strength of 150,000 PSI for all diameters, and are offered in two types.

In Fact 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 inches (13 to 38 mm) in diameter.

In accordance with ASTM A325, all threaded components of the fastener assembly must be galvanized by the same process and the supplier’s option is limited to one process per item with no mixed processes in a lot.

This Specification deals principally with two strength grades of high-strength
bolts, ASTM A325 and A490, and with their design, installation and inspection in
structural steel joints. Equivalent fasteners, however, such as ASTM F1852
(equivalent to ASTM A325) twist-off-type tension-control bolt assemblies, are
also covered. These provisions may not be relied upon for high-strength fasteners
of other chemical composition, mechanical properties, or size. These provisions do
not apply when material other than steel is included in the grip; nor are they
applicable to anchor rods.
This Specification relates only to the performance of fasteners in structural
steel joints and those few aspects of the connected material that affect this
performance. Many other aspects of connection design and fabrication are of equal
importance and must not be overlooked. For more general information on design
and issues relating to high-strength bolting and the connected material, refer to
current steel design textbooks and the Guide to Design Criteria for Bolted and
Riveted Joints, 2 nd Edition (Kulak et al., 1987).

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