These are parts from Saya Koubou, a well-known online retailer of handmade parts. Made of surgical stainless steel, they are resistant to discoloration and unlikely to cause allergic reactions. They are free size and, for surgical steel, are very soft and easy to adjust. They are cute as they are, and you can also pour resin freely into the star-shaped areas for added customization. They are 420 yen each + shipping on the official website. Currently, no price reduction is possible. Shipping will be via standard mail, so it will take a few days.