The connections that secure the brake line to the brake system are called fittings, and the size and type will be specific to the make of your Isuzu NQR. When replacing brake lines, these connections will need to fit with the area of installation but also be crafted from an appropriate material.
The fittings for the brake lines on your Isuzu NQR are gauged by several factors. With the help of calipers, you can measure the thread diameter and determine either a male or female thread. You also need to identify the end configurations and the grouping that will be needed for installation.