ASTM A307 is the starting point for hex head industrial fasteners. It covers the most common bolting used in flanged piping systems, and in much of the equipment ancillary to the pipelines. A307 has several grades. Grade A is supplied in a finished hex pattern.

ASTM A307 Grade B is a heavy hex pattern. It differs from ASTM A307 Grade A in two key ways: the first is the heavy hex pattern, allows the load to be spread over a wider surface (also, since washers are less common in flange applications, this is another common reason for Grade B). The second is that A307 Grade B has some max strengths rating that Grade A doesn’t have. At first glance, this may seem contradictory, since Grade A can be stronger than Grade B. However, piping systems include a variety of critical equipment, and the Grade B spec is there to allow a bolt to flex or break rather than another component.

Per the ASTM specification, grade B is the recommended spec for CI flanged systems, although the industry still uses grade A more commonly.

Grade A is typically supplied in zinc finish (most common on flanges), plain finish (most common on equipment that will be painted) and hot dip galvanized (often in sizes smaller than 1/2″ that are used on industrial structural applications that do not fall under ASTM A325). Grade B is typically supplied plain. Zinc has only recently been readily available for Grade B. HDG Grade B bolts are least common, especially with the emergence of Grade B zinc.

Technical Threads stocks both Grade A and Grade B in all three of the common finishes. Additionally, we can supply special coatings, such as blue Teflon or Xylan per application.