O-Rings of Buna-N. A firm, rugged, flexible, Nitrile Elastomer. These are great for putting on 1mm, 2mm or 3mm cording to hold beads in place. So they are marked as such, after fitting them to our Buna Cording. We've also listed their exact inner diameter and outer diameter for you. Also, great for spacers or to use as jump rings in jewelry! These are super cool! How about embedding them in resin or using them inbetween fused chain links?