An Open jump ring has a cut in the ring so you can open and close it.

Use them to attach a clasp, a charm,  or a grouping of items together.

They are available in a variety of sizes, materials as well as gauge (thickness of the wire).

The larger the number the thinner the gauge. (ie. an 18 gauge ring is much thicker than a 24 gauge ring).

The most useful item in your bead kit!