Miracle Magic beads
I have been using magic beads for a many years now and when I was designing swimwear I was known for adding magic beads to the end of bikini ties. I bought most of mine whilst on work trips in Sham Shui Po, a district in Hong Kong that is full of trim and fabric shops. They are called miracle magic beads because of the 3-D illusion effect, it looks like there is a bead within the bead.
You can find them on Etsy and Ebay from many sellers in an abundance of colours and sizes.