The ring band is open on the bottom, but it's not intended to be adjustable but can adjust a little.  

Laser cut and hand assembled
Height x Width: 1 in x 1 in 

80% Acrylic Resin (Design), 20% Brass With Imitation Rhodium Plating (Metal Ring)

Small:  15.7MM Fits best ring size 4-5.5

Medium: 17.3MM Fits best ring size 6-7.5

Large: 18.9MM Fits best ring size 8-9.5

Please be aware that resin is akin to ceramic and glass, and therefore may be damaged if dropped or knocked. Keep your Erstwilder jewelry neatly tucked away in your gift box when not being worn, avoid contact with perfumes, lotions, water and excessive sunlight, and you’ll have your piece for years to come. Clean gently by hand.