Thread standard is where most of the confusion lives. NPT, JIC, AN, metric O-ring and SAE flare are not interchangeable, and a fitting listed as 1/4 inch may mean the thread or the hose inside diameter depending on the standard.
Every fitting states its thread size and style. Hose lists inside diameter, outside diameter and working pressure where published. If you are building a line from scratch, match the thread standard first and the size second.
