Cork and Silver Ring and yes it is adjustable. Hand made in Portugal. 

Cork is one of the most highly renewable and eco-friendly resources on the planet. It is harvested only from the bark of the cork tree, which means the tree keeps on living and helping to clean our air. Additionally, the bark grows back in about 9 years at which time it can be re-harvested.

It doesn't harm the tree, and the cork bark regrows. Most cork forests are in Portugal and Spain. The year of harvest is marked on the trunk, so each tree isn't harvested at the wrong time.