This cool little piece looks like it melted together at one time and then totally smoothed in the sea. It's definitely as one of a kind as sea glass gets.
I make the pendants on a single piece of Sterling wire with a loop on the top that can accommodate most average size chains if you wish to switch it out. It will come on an adjustable sliding knot cotton cord.
All the sea glass I use is just how I found it (except for drilling a small hole). You can't make genuine sea glass in a machine as it takes years and years to be smoothed by the wind, waves and sand, also the surface forms a unique and layered frosted surface that captures the light with so much more texture.
You'll see the measurements on the second photo. This is small but nice and round. Just an inch or 2.5cm total length.