Please read the profile! Important notes are included. Purchase = Agreement. Finger ring sizer, one color (different colors are also on sale) I'm a novice, so I can't answer detailed questions about the materials... Please understand that it's discounted accordingly. The approximate size is shown in the photos, so please use them to judge. (※The inner diameter of the finger ring sizer is 16mm-17mm.) For the finger ring sizer, you can use jump rings or C-rings that match the groove thickness. What is a finger ring sizer? It's a craft tool used to open and close or hold parts like jump rings and C-rings. You wear it on the thumb of your non-dominant hand. How to use a finger ring sizer: ・Put the finger ring sizer on the thumb of your non-dominant hand. ・Insert a jump ring or C-ring into the groove of the ring. ・Use flat-nose pliers or pliers to open and close the ring by moving the cut part of the ring back and forth. It's a very useful tool for making accessories(^^♪ Thank you for your consideration.