This is an overview of "Spring" type snaps, also known as S-Spring,
There are different types of snaps with the most three most common used by bagmakers being --Spring Snaps (Fashion weight and come in more colors/finishes), Line snaps (utility-weight), and Magnetic snaps (which come in assorted weights/strengths).
Spring snaps are finer looking, come in a larger variety of colors/finishes and good for garment-weight and lighter-to-medium weight materials. Line snaps are stronger and good for leather and heavier (utility) types of use. Having said that, you can go up in the size of a Spring snap to increase its' holding security.
Download this 3-page PDF with simple diagrams that depict SPRING SNAP sizes, which snap goes with which snap die on your press, and a how-to-install a spring snap using a Table Press such as Kam.