The base inner diameter is 16mm. Only size adjustments down to 13-16mm are possible. For sizes larger than 16mm, please confirm if it's possible before purchasing m(_ _)m Blue Moonstone: 9mm (late) Feather Fluorite: 13mm ※ Blue Moonstone is said to have the effect of controlling emotions that change like the phases of the moon. It is said that those with intense emotional fluctuations will find emotional stability by wearing blue moonstone. It is especially recommended for those who are easily irritated or prone to stress. ※ Feather Fluorite provides the power of "healing" and a sense of security as if gently enveloped by angel wings, relieving fatigue and stress. It will help to alleviate the anxiety you are currently feeling and reduce stress. It is also recommended as a healing stone for those who tend to overwork themselves or have accumulated mental and physical fatigue. Not compatible with metal allergies ( ´._.`) This is completely handmade, so please understand before purchasing. ※ Please check the images carefully and make your own judgment. If you have any questions or concerns, please ask before purchasing. Returns, refunds, and exchanges are not accepted after arrival. I make these by hand! Please understand. If you are looking for perfection, please purchase from a shop. (※) Price includes shipping, packaging, and handling fees. (※) No discounts during time sales. If you would like a regular discount or a discount for multiple purchases, please leave a comment. m(_ _)m Requests without a comment will be rejected. Please also read the profile (♡ᴗ͈ˬᴗ͈) I do not accept custom orders, only size adjustments.