This ring appears to be a button that is fastened through it's hole. In fact, the button and hole are made from one continuous piece of stainless steel that is made using 3D printing technology. The ring is adjustable because the "button" end is not attached to the "hole", but passes clear through. 

Some of the pictures show the button "sewn on" with thread. The thread doesn't actually hold the button on, it's purely decorative. You will receive one ring in the sizes and color of your choice (see below) AND a free 20-piece sewing kit which includes thread and needles so you can sew your button on many times to match your outfit or mood.