Hello, I am guessing the 1/4 and 5/16 are bolt sizes, so the openings across the flats would be 7/16" and 1/2" respectively?? 12mm would be approximately 15/32", just 1/32" greater than 7/16". 14mm would be 17/32" , 1/32" greater than 1/2". Something to do with the sloppy tolerances on the bolt sizes? Or, one wrench will work for 7/16", 1/2", 12mm, and 14mm? Regards, Lou