1/25 scale - 3/4" or -12 AN larger fuel or oil lines.
1/16 scale - 3/8" or -6 AN - typically used for smaller fuel or oil plumbing.
1/12 scale - 1/4" or -4 AN - typically used for brake line applications, small oil lines, some small fuel line applications like nitrous, pressure gauges and vacuum lines.
1/8 scale - Less than 3/16"
The scale size is determined by its outside diameter (OD) compared to real world braided line since an inside diameter isn't useful in scale modeling. See the tables in the section called LINKS, INFO & TECH.
Use .035 Pro Tech hex fittings or Size C1 or C Silver ferrules.
Each package contains one coil of .035 x 18", by Pro Tech.