The ring in the photograph:
This size adjustable bullet ring (which is similar in its design to the Quad Side Stone Ring) holds a large replaceable Swarovski crystal at the center and four smaller (irreplaceable) stones decorating the periphery (display stones not included - can buy separately)
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Item dimensions:
1.20 x 1.25 x 1.30 inches
(dimensions may vary per size)
 
Replacing the Center Stone:
1-Carefully insert the Allen wrench into the side of the ring and turn counter-clockwise to unlock the stone.
2-Press the end of the Allen wrench onto the back of the ring to release the stone from its base.
3-Place the new stone inside the ring and gently press down to ensure it is securely placed.
4-Insert the Allen wrench again into the side of the ring and GENTLY turn clockwise to lock the stone in place (do NOT forcefully turn any more than necessary - mechanism inside might break).
 
Casing Type: 
416-Barrett
50 BMG
 
Ring size:
6-13
 
Center Stone:
All 20
 
Plating Type:
14k Gold
14k Rose Gold
Palladium