PICTURES ARE REPRESENTATIVE OF ITEM, BUT ARE NOT OF THE ACTUAL ITEM. Product dimensions, finish, head markings, thread length, stamping shape or forging shape, etc., may differ from picture. Products are guaranteed to meet the specifications to which they are manufactured. Specifications allow for tolerances in dimension and shape, which can vary from lot to lot. Jam nuts are tightened against the work surface and a full heavy hex nut is tightened against the heavy hex jam nut to keep it from loosening. Steel nuts shall be made from a low carbon steel which conforms to the following chemical composition Carbon: 0.47% maximum; Phosphorous: 0.12% maximum; Sulfur: 0.23% maximum . Grade 2: Rockwell C 32 maximum. Grade 5: Rockwell C 32 maximum. Grade 8: 1/4 thru 5/8” Rockwell C 24-32; Over 5/8 thru 1”-- Rockwell C 26-34; Over 1 thru 1 1/2”-- Rockwell C 26-36 .