What are stitch markers anyway?? That is the most asked question by people who are not knitters or crocheters, along with people who are. According to Wikipedia,
A stitch marker is a mnemonic device used to distinguish important locations on a work in progress.
So, they designate the beginning of a row, pattern repeat, etc. Stitch markers are placed on knitting needles with rings so they slide from one needle to another. For crochet, a single hook is used to create the fabric so a Progress Keeper is needed to mark places. A progress keeper has a clasp that opens and closes, catching stitches.
You will notice in my listings that there are options. A Ring Clasp is an attachment that can be used as both a ring marker and a progress keeper as well as an earring! There are also two sizes of soldered rings for knitters, one small for sock knitters who use small diameter needles and another for more common knitting.
Below I have graphic for some of the many uses and a short video showing how ring markers work.