Advantages: produced for drilling with uniform wall-thickness, wall thickness deviation +/-5%. High dimensional accuracy and nice straightness, straightness 1/1000mm or 0.5/1000mm. Reliable performance (including hardness) and nice torsion-resistant. Main standards: astm a519, din. Main materials: 4130, 4135, 4140, 30crmo, 35crmo, 42crmo, 34crmo4. O.D. 30 to 127mm, W.T. 5 to 13mm For qt condition: Tensile strength>=1030mpa, Steel strips bundled, cover with plastic fabric, woven bag packed
