The inside is engraved with "STM 316L" and it is made of surgical stainless steel, which is also used for medical instruments. It is resistant to rust and discoloration, so you can wear it in the bath or at the sea without taking it off. It is also a gentle material for those with metal allergies. *As this is a used item, quality is not guaranteed. Please refrain from bidding if you are looking for a perfect item or are sensitive about condition. *It is difficult to list all scratches and defects of the product, and there may be oversights in addition to the listed information, but please accept it as no claim, no return. *Please judge from the images and photos before bidding. *The items for sale are stored by an amateur and will be packed simply. *I cannot answer technical questions. *I will answer questions to the best of my ability. *To prevent fraud, please accept it as no claim, no return. *Please be careful when bidding, as cancellations or holds after bidding are not accepted. *Please refrain from asking questions after bidding or winning the auction. *Please contact us within 24 hours of winning the auction. *Please only bid if you can make payment within 24 hours. *We will ship via RakuRaku Mercari便. *The information listed above is for tracking numbers and delivery methods; only the shipping methods listed in the shipping details are available. *We are not responsible for any loss during shipping. *We do not issue receipts.