scope:

These specifications cover two types of steel tubing suitable for automotive uses. There are requirements for the base metal, the optional coating materials, and the coated tubing. These requirements are applicable to the product coming out of the tube mills and the coating application lines, which are sometimes separate facilities. This tubing is used in the production of customized parts and assemblies. It is recommended that those parts and assemblies be validated for corrosion performance, conductivity and continuity, strength, appearance, and other critical properties unique to the particular application.

GM123M. Covers double wall construction tubing wherein the two walls and the joints are copper brazed in a reducing atmosphere to produce tubing satisfactory for hydraulic lines. It should not be used for fuel lines because residual copper can contribute to the formation of sour gas. See Figure 1.

GM124M. Covers single wall construction tubing wherein the joint is electric resistance welded. It is recommended for fuel lines, power steering lines, transmission oil cooler lines, lubricating oil lines, vacuum lines, etc. See Figure 1.

Tubing Designation Code. It is recommended that the codes in paragraph 3.1 be used on drawings and purchase orders to designate tubing type, outside diameter, wall thickness, manufactured condition finish and the internal diameter (ID) coating.

Typical Application. GM123M is typically used for hydraulic brake lines whereas GM124M is typically used for fuel lines, power steering lines, transmission oil cooler lines, lubricating oil lines, vacuum lines, etc.