Steel Grade and Mechanical Property Customization: Both seamless steel tubes and rebar couplers can be customized under requirements of steel grade, size, MECHANICAL PROPERTY and surface quality. Steel grade follows international standards ASTM A519, ASTM A106, ASTM A500, ASME SA500, DIN2391, DIN1629, EN10305-1, DIN17121, EN10297-1, JIS3441, JIS3444 and JIS3445.