Aren't they 13 mm bolts, but anyways what you need is to get your hands on a neumatic gun, when i changed mine i just cut it in between the muffler and resonator to take care of the back end of the exhuast, but i used wd-40 and pertrolium oil to break the rust at the catalytic converter and after an hour or so of trying to break the bolts by hand i remember my neighbor had a neumatic gun so i grabbed my air compressor and had the nuts off with no problem at all.