This specification covers double-wall, copper brazed steel tubing suitable for general engineering uses, particularly in the automotive, refrigeration, and stove industries for fuel lines, brake lines, oil lines, heating and cooling units, and the like. The tubing shall be made by rolling steel strip into the form of tubing and subsequently copper brazing in a reducing atmosphere. The steel shall conform to the prescribed chemical composition and shall be subjected to heat analysis and product analysis. Tension, flattening, expansion, bending, and pressure proof tests shall be made in accordance with the specification.