ZipNFC ANTI METAL 29mm Round Disc/Tokens in black ABS plastic, 5mm in height and a larger hole in the middle than our standard black ABS discs.  The  ANTI-METAL protention is INSIDE the disc and a very sticky 3M backing. These are manufactured for business and used for commercial use so very strong and durable as well as having a strong adhesive applied. They also have an excellent reading distance. They are weather proof, waterproof, dust proof and can be placed on Metal surfaces so can be used outside as well as inside. These have a larger hole in the centre that enables you to screw or nail them to surfaces. These are rated as IP66.