This black rubber line is extremely soft, bends easily and it cannot kink. 

Since it is not solid and not a wire, it will drape like a line real.

This soft line equals the following equivalent 1:1 size at each scale.
1/25 scale = 1 5/8"
1/16 scale = 1"
1/12 scale = 3/4"
1/8 scale  =  1/2"

Depending on your scale, typical uses are coolant, fuel and oil lines.  Also, at larger scales, A/C lines to/from the compressor and fuel supply and return lines to/from the fuel cell or gas tank.

Use Pro Tech Hex Fittings sized at .060 or search this site for 'ferrule' fittings.

Each package contains 12" of .068" black line, by Ted's Modeling.