hey all,
i have stashed some cables and housings without labelling what they were for. if it's feasible, how can i visually indentify road/mountain, brake/derailleur housings or cables?
thanks!

and a reasonable corollary question would be, when, if ever, does it not matter which use the cable or housing was intended for?

Der cabling isn't strong enough for brakes.
Brake cabling is overly stiff for der use.

Brake cable is spiral wire wrapped, derailleur cable is straight wire wrapped. Typically brake cable is 5mm while derailleur wire is 4mm as well.

Slightly flex the housing. You can see the spiral wire in a brake housing, but not shifter cable housing.

The inner cables will have ends that are peculiar to their intended purpose. Mountain brake cables, for example, won't fit road brake levers.

Derailleur inner cables are usually thinner and the end fittings obviously different from brake cables.

Derailleur cables often have a different fitting at each end, one for road bike shifters and the other for MTB shifters and you cut off the end you don't need. Some derailleur cables have two different "road shifter" fittings, one for Shimano STI's and the other for Campy Ergo's (they are slightly different diameters), and again you cut off the unneeded one.

Brake cable housing (spiral wound) can be used for derailleurs but it's isn't ideal and may compromise index shifting performance.

Derailleur housing (straight reinforcing wires) should NEVER be used for brake housing as it's radial strength is inadequate.

Don't you mean brake cables? Shimano equipped bikes use the same shift cable for both road or mountain shifters.

No, I meant shift cables but I thought that Shimano MTB and STI shifters used a different end fitting. Maybe my memory is faulty since I haven't worked on MTB shifters in years.

I am sure about the double end road shift cables since I have and use them for both Ergo and STI brifters and the fittings are similar but not identical.

thanks guys, that was quite helpful!