This set--an exclusive at Glass Art Tools--is specially designed for use with Colors for Earth outline liquids, which come in either black or white (available on GAT's Colors for Earth page). The tiny hole in the black tip allows you to create thin, flowing lines, detailed decorative designs, tiny dots, even handwriting.
Note that this set contains no bottles, because the caps fit directly on your bottles of CFE Outline Liquid. (If you need them, empty 1-oz bottles are also available here at Glass Art Tools).
Each of the two fine tips can be screwed onto the top of the red cap. CFE warns: Don't screw the tips on too tight! A gentle tightening is all that's needed. When you've finished using the paint, unscrew and rinse the tip and replace it with the clear plastic top that comes with the cap. That will seal your bottle if you plan to use it again.