This is a black nylon-coated stainless steel multi-strand wire.

It is slightly springy and can be bent at sharp angles
The OD dimension is .010" or .25mm. 

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

Typical uses are small oil lines, vacuum and fuel lines, especially fuel & nitrous delivery at the the carbs, blower manifold, injector plate or injectors.  

Each package contains one coil of .015" x 18" soft line