Grade 2H nuts are recommended for use with bolts in high-pressure and high-temperature service Grade-2H nuts are heat treated by quenching in a liquid medium from a temp above the transformation temp Rockwell C24 - C38 150 000 psi proof load Hot dip galvanizing is generally the most effective way to apply a sufficient thickness of zinc to threaded fasteners for zinc to serve as a corrosion protection in harsh enviroments.