In the past ASTM A325 was specific to heavy hex head bolts only. Under the ASTM A325 specification, this is still the case, however with the implementation of ASTM F3125, things have changed. F3125 still states that the bolt be used in a steel to steel connection, however it allows for the head to be something other than a heavy hex pattern under supplemental requirement “S2”, such as square head, carriage bolt, etc. This also includes head styles such as timber bolt heads.
It is important to keep in mind that if the head configuration is different than a heavy hex, the head of the bolt must be stamped “A325S”. Although the F3125 Grade A325 specification allows for these different head styles, it is important to confirm with the Engineer of Record that the head style will work for the application. ASTM A325 being specified does not necessarily mean that they will allow for the supplemental requirement found in ASTM F3125 Grade A325.