What's the Difference in Bolt Grades? 

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.

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.

Can I Use One Grade Over the Other?

So the question we hear most is "can an SAE J429 Grade 5 be used when an ASTM F3125 grade A325 is specified?"

The answer is NO. Why you ask? Because grade A325 and A490 bolts are produced with a heavy Hex Head configuration which provides a wider bearing surface that helps to distribute the load applied to it. Grade 5 and 8 bolts are produced to the standard Hex Cap screw configuration and therefore cannot distribute the load as much as is needed for structural applications, such as a tower structure. In addition to the enhanced bearing capabilities, 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 Bbolt 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.
 

Replacement Rohn Hardware & Rohn OEM Bolt Kits

Though most Mounts come with the minimal amount of Requisite Hardware, it by no means accounts for all Mounting Options, Materials and Custom Installation Scenarios. Take a moment to Consider the Options and Materials in Use. Then Select the Appropriate Hardware to realize your Goal. The Flexibility and Longevity of any Mount to Match the Mounting Conditions may depend on it.