4PCS Colorful 125khz Rfid Waterproof Proximity ID Card EM card RFID wristbands bracelets and wrist band ID TK4100 silicone id wristband (4colors) Frequency: 125KHz Chip: TK4100 Material: Silica gel Size:Outer diameter 74mm; Inner perimeter 20cm Waterproof, moisture, shock, high temperature resistance Closed-loop wrist strap, flexible, easy to wearing and easy to use Applies: swimming pools, cooling libraries, sauna bath center, supermarket, playground, children's park, ticket system, etc