Both ASTM A490 and ASTM A325 Bolts are heavy hex structural bolts. Do you know the difference between ASTM A490 and ASTM A325? Today, let’s talk about it.
The simple answer is that ASTM A490 heavy-duty hexagonal bolts have higher strength requirements than A325 heavy-duty hexagonal bolts. A325 bolts have a minimum tensile strength of 120ksi, while A490 bolts have a tensile strength range of 150-173ksi.
In addition to this, there are some other differences between the A490 and A325.
Material Composition
- A325 structural bolts are made from high-strength medium carbon steel, and the most common bolts found in building construction
- A490 structural bolts are made from high-strength heat-treated steel
- A325 structural bolts can be hot-dip galvanized and are commonly found with that coating. A325 galvanized bolts are popular due to their corrosion-resistant properties.
- A490 structural bolts are stronger, they cannot be hot-dip galvanized due to this strength. Due to the high tensile strength of A490 bolts, they are at risk of hydrogen embrittlement due to galvanizing. This can lead to premature failure of the bolt and may become structurally unstrong.
Coatings
Configuration
Both A3125 and A325 bolts fall under the ASTM F490 specification and are specifically used for structural bolts. Typically, structural bolts are heavy-duty hex bolts or tension control bolts that are typically shorter in length, shorter than the average thread, and cannot reduce the body diameter.
According to the norm, some exceptions are allowed. Prior to 2016, ASTM A325 and ASTM A490 were separate specifications. They have since been reclassified as classes in the F3125 specification. Initially, the A325 and A490 bolts had to have a heavy hex head and no other configurations were allowed. In addition, the short thread length cannot be changed.
However, according to the new F3125 specification, any head style is allowed and the thread length can be changed. Changes to the typical A325 and A490 configurations are specified by adding an “S” to the permanent slope marker for the head.
Another difference in thread length is that A325 bolts are mass-produced in a full-threaded version, provided they are four diameters or less in length. This type of bolt is commonly referred to as A325T. The fully threaded version of this A325 bolt is not available for A490 bolts.
Testing
A325 galvanized bolts that are being purchased with a nut and hardened washer are required to be rotational capacity tested. A rotational capacity test ensures the bolt assembly is capable of developing the proper clamping force. To pass the test, the assembly must reach a minimum amount of rotations and achieve the required tension before failure which depends on the diameter and length of the galvanized A325 bolt. Since A490 bolts cannot be galvanized, this test is not applicable.
All A490 bolts must pass a magnetic particle test. This test is used to ensure that there are no sub-surface defects or cracks in the steel of the A490 bolt. This test is not required for A325 bolts
ASTM A490
Bottom Line
Ultimately, your engineer will specify which grade of F3125 structural bolt you need to use, but it’s important to understand the difference between A325 and A490 grades. The A490 grade is stronger than the A325 grade, but strength is not the only factor that determines a bolt. A490 bolts cannot be hot-dipped or mechanically galvanized. The A325 grade is not as strong, but it is a lower cost bolt that can be galvanized to avoid corrosion.
Post time: Jan-31-2024
