Dito to what MoDoc said, except for the use at the machine shop, I used to use them at the machine shop I worked at until I was laid off in January. But beside that they can be really handy and I even like to use them a lot for coloring the back of nymphs that I tied with tyvek, few dots with a dark color them color the top of the whole thing with a light color and bam... mottled nymph back.

Steve