They are not the same, and since this is a 'safety issue' not sure that 'your thoughts please' is appropriate. Companies suggesting 'universal outers' are talking utter and dangerous BS.
Sheldon
Gear cable outers need to resist compression so the metal strands are longitudinal. Brake cable outer (metal element) is a tightly wound helix. Use of a brake cable outer for a gear cable will screw up the indexing. Use of a gear cable outer for a brake cable may result in failure and an ineffective brake
![Oh my! :ohmy: :ohmy:](/styles/default/xenforo/smls/ohmy.gif)
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Also different inner cable diameter.
Mexhanical (and hybrid (mech/hyd) disc brake cables benefit from 'compressionless' outers to improve performance.
Sheldon: "Warning: Since compressionless housing relies on plastic to hold it together, it is not as strong as conventional spiral housing, and should never be used for brakes! The loads applied to brake cables can easily cause compressionless housing to rupture and burst, causing a
complete and sudden loss of brake function. "