In order to provide a reasonable answer you would have to at least tell us what the application is. Then, even if you don't know which code is applicable, we can at least make a wild guess as to which code is appropriate for the application.

Marshall, check your reference. The clause cited (3.7.3.2) is a subordinate clause of 3.7.3 for unpainted weathering steel. Table 3.7 of D1.1-2006 would be more appropriate for general structural applications. The size of the single pass fillet weld is dependent on the welding position as well as the process if D1.1 is applicable.

If D1.1 is applicable, Table 3.7 lists the following maximum size limitations for single pass fillet welds:

Flat - 1/2 in.
Horizontal - 3/8 in.
Vertical - 1/2 in.
Overhead - 5/16 in.

Not only should you be cognizant of the maximum size single pass fillet welds, but you should be aware of the minimum single pass fillet weld sizes based on the thinner of the two base metals being weld. Table 5.8 addresses those requirements if you are using a recent edition of D1.1 for a structural application.

Best regards - Al