A325 and A449 bolts are virtually identical in mechanical and chemical properties through 1” in diameter. However, there are a few important differences between the two grades. The diameter range, configuration and mechanical properties above 1” in diameter are the main differences.

A325 bolts have a diameter range from 1/2″ through 1-1/2”. The specification requires the fasteners to have a forged head on the bolt. Due to their application, they have a shorter thread length than a typical heavy hex bolt. These bolts are designed to be used in structural steel connections.

A448 bolts have a diameter range from 1/4″ through 3”. These bolts are not limited to a specific configuration and can be made in any form of fastener. The strength properties of A449 above 1” drop significantly compared to A325 which makes them an unsuitable substitute in larger diameters. 

A449 & Grade 5 are virtually identical in mechanical and chemical properties. Grade 5 bolts are designed to be used in automotive applications. These are tight-tolerance, precision-quality cap screws. The diameter range is 1/4″ through 1-1/2”. These are mass-produced fasteners with standard hex heads. 

A449 bolts are not limited to a specific application and also have a much larger diameter range of 1/4″ through 3”. This grade of steel can be manufactured in any configuration and is not readily available in the marketplace. 

The difference between these two types is due to the material used to manufacture them. Type 1 is a carbon or alloy-based steel that will rust and corrode over time if exposed to natural elements. The Type 3 material is a weathering steel that has natural atmospheric corrosion resistance properties and will rust over time as a way of protecting the steel from corroding. A449 type 3 fasteners are not readily available in the marketplace due to a lack of raw material availability.