Choose "skinny" caps for a thin, concentrated line for outlining and fine detail work. The Montana Superskinny #1 is a popular choice in this area as is the Montana Skinny Banana, also known as German Outline. Caps also come with a variety of colored "dots," the outlet on the cap from which the paint sprays. Gray dots and black dots deliver thin lines.
Select "fat" caps for broader, fatter lines and for filling in large areas. German Fat and New York Fat are popular choices, as are orange dots and pink dots.
Choose a calligraphy cap for signatures and other smaller-scale writing. These caps have a rectangular dot that delivers more spray at the top and less at the bottom. Some can be flipped from vertical to horizontal for varied looks. Montana has its own calligraphy cap, but there are generic ones that are compatible with Montana's paints.
Pick gold caps and blue caps for softer sprays. These are poor choices for outlining, but work well for blending colors and stencil work. They produce a medium line with a softer outer edge.
Adjust spray by moving closer to or farther from the canvas. This will work with some paints, with the line becoming narrower the closer you get to the target. However, with many paints, getting closer will just result in the paint running.