describe: key chain! This is a compact and super customized key solution. This product does not contain metal noise. It is used to sort and store key chains. In addition, this product is not limited to keys. As long as the user likes, U disk and RFID chip can be integrated together. The inner diameter of the column is 4mm. Make sure that the inner diameter of the lock is greater than 4 mm. The height of the internal standard column is 11mm (4-5 commonly used keys can be placed). If there are special keys, please measure in advance. You can install keys (the thickness is equivalent to 3-4 ordinary keys), you can also install vinyl head keys, you can also install plastic insertion points or galvanized directly. Compact design: smaller than a pack of bullets. Put it in your pocket. No noise: The buttons no longer jitter, avoiding metal noise. Label: Yes Material: Aluminum alloy after sandblasting and oxidation treatment. Process: stamping + anodizing. Material: 6061-T6 aviation aluminum. The package includes: 1 smart key key ring. Product Type: Key Wallet notes: Due to manual measurement, please allow measurement deviation. Due to display differences and lighting effects, the actual color of the product may be slightly different from the color shown on the picture. Thanks! Package: 1*key wallet