This specification covers chrome-molybdenum (4135) seamless steel tubing of aircraft quality. Classification: Tubing shall be of the following types and physical conditions@ as specified (see 6.2): Type I - Round Type II - Rectangular or square Type III - Streamline Type IV - Oval Physical condition: (A) - Annealed (N) - Normalized or stress relieved (HT-125) - Heat treated to a minimum tensile strength of 125@000 psi (HT-150) - Heat treated to a minimum tensile strength of 150@000 psi (HT-180) - Heat treated to a minimum tensile strength of 180@000 psi (HT-200) - Heat treated to a minimum tensile strength of 200@000 psi Unless otherwise specified@ tubing shall be furnished in type I@ condition (N).