This is the silver holder for the full colored Sandstone inserts.
Once you have puchased and recieved your Silver curved necklace and Sandstone insert. Thread a chain or leather strip/necklace through the holes at the ends of the holder, then insert your sandstone carefully in to the holder, it is a tight fit so it will stay in the holder.
Try inserting an end first then ease the rest in, one end may work better than the other. I have tried all 4 Sandstone inserts in the holder they do all fit, a little pressure will get them in safely. If you are struggling you could use a sandpaper nail file to take a little off the sandstone (I only needed to do this on the prototypes).
The holes in the back of the holder are there to help take the Sandstone insert out, so you could swap for a different color Sandstone insert. Use a metal nail file or small flat scewdriver to carefully leverage the sandstone out, lift it just a little at a time working your way along the insert, don't rush it. The Sandstone is quite strong.