Specifications Hign-concerned Chemical:None Model Number:13.56MHz CUID Origin:Mainland China Certification:CE Black Waterproof Ring IC 13.56Mhz CUID Smart Chip NFC Android App MCT Rewritable Tag Badge Clone Key Card Copy Caution: This link is for a single chip, not dual chips, please check the details page to purchase The IC chip (13.56Mhz) is a CUID chip. (Please make sure the machine supports writing to CUID card) Professional Duplicator When Copying, If You Need, Please Contact Customer Service. About Size: circumference 53MM, diameter 16.5MM circumference 56MM, diameter 17.3MM circumference 59MM, diameter 18.2MM circumference 62MM, diameter 18.9MM circumference 65MM, diameter 19.8MM Regarding The Appearance, It Is Basically In Line With The Picture. If There Is A Slight Deviation, Please Refer To The Actual Product. Packing: Smart Ring If You Have More Questions, Please Contact Customer Service. Specific measurement methods: Please use a thin line or paper strip to measure the circumference of the finger wearing the ring, and select the number corresponding to the size chart above. 1. Use a thin, non-elastic rope. 2. Make a circle around the place where you wear the ring and tighten the measuring line. 3. Use a ruler to measure the length of the rope. Precautions: 1. Use thin paper strips or ropes to measure the position of your fingers. Do not measure the finger joints. Make a mark where the paper strips or ropes overlap. 2. During the test, be sure to tighten the paper strip or rope, measure multiple times and take the average, and control the error within 1MM to avoid abnormal differences.