The base inner diameter is 16. Only size adjustments down to 13-16 are possible. For sizes larger than 16, please confirm if it's possible before purchasing m(_ _)m I post videos on Instagram ▶︎ ichigohime__ Please read the profile before purchasing. ※ The effects of aquamarine are known to include stress relief, mental stability, building good relationships, and as a talisman for "happy marriage." It is considered a versatile stone that calms the mind, enhances communication skills, and is also used for safe travel, especially recommended for those entering a new environment or wanting to smooth out relationships. ※ White garden quartz is a power stone believed to be effective for purifying the mind, relieving stress, and providing mental stability. It promotes relationships and business development, and can also ward off negative energy. It is also said to aid in grounding and attract wealth, making it popular with business owners and the self-employed. I do not accommodate metal allergies, but if I have the stone in stock, I may be able to remake the item without the metal parts, so please check before purchasing ( ´._.`) As it is completely handmade, please understand and purchase accordingly. ※ Please check the images carefully, make your own judgment, and ask any questions or address any concerns before purchasing. Returns, refunds, and exchanges are not accepted after arrival. I am a handmade seller! Please understand. If you are looking for perfection, please purchase from a shop. (※) The price includes shipping, packaging, and handling fees. I do not understand requests for discounts on combined purchases based on the shipping cost, so they will be rejected. (※) If you would like a discount or a discount on a combined purchase, please leave a comment m(_ _)m Otherwise, it will be rejected. Please also read the profile (♡ᴗ͈ˬᴗ͈) I do not accept custom orders, only size adjustments.