Each model train track comes with various codes or sizes for each scale. These codes are identified with numbers which translate into the height of the rail track in inches. For example: Code 100 – gives you 0.1 inch height and 156lb rail. In the same way, Code 83 – gives you 0.083 inch height and 132 lb. rail.
When it comes to creating a prototype track, the main lines are made with heavier rails and the branches or deviations are made with lighter rails. The roadbed and the space between ties of these codes vary as well. For example if the mainline needs 24 ties/39 foot rails, it comes down to 11 1/2 inches between each tie. With this in mind, use heavy code rail for the mainline and smaller code for the sidings.