Most cars use 3/16 line front and back. Some use 1/4 to the back. The master has two different size fittings so the guys who put the car together don't mix the brake lines up. Lots of time the brake line is the same size(usually 3/16) and only the fitting itself is larger. Adapters, 3/16 brake lines with the larger fitting and the fitting only (for 3/16) are usually available. Check with NAPA or other parts house.