7/16 UNF(unified national fine) is the standard used.This is obviously a fine thread.You can also get UNC(unified coarse).There is a genuine reason for using a fine thread although i cant remember what it is/was.
Personally i would go for the 7/16 UNF or if you cant get them then go for M12 in a fine pitch,M12 by 1.50 pitch as opposed to the standard M12 by 1.75.Although probably easier to get the UNF thread than a metric fine.
(8.8 tensile strength or 12.9)