A449 and Grade 5 bolts are virtually identical in mechanical properties. There are a few slight differences between the two grades though. 

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.