Band width at underside is 3.9mm. If you are looking for something specific just contact me I will see if we have the item in our extensive range of stock. Our company has been involved in the Opal industry for over 25 years in everything from mining right through to sales.We are a registered Australian Business and are located in Adelaide, Australia. All our products are genuine opal as described. We believe in building our business on trust and communication with a desire to create long term customers. This item is in the category "Jewelry & Watches\Fine Jewelry\Rings". The seller is "opalwholesalers" and is located in this country: AU. This item can be shipped worldwide.