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An open metal card case
A card enclosure is a container for smart cards, credit cards, debit cards, telephone cards, visiting cards, business cards and other cards of similar size. Most cards have dimensions that follow the ID-1 format of the ISO/IEC 7810 standard which specify the physical dimensions for cards to be 85.60 × 53.98 mm. The enclosures can be made of metal, leather, or plastic and come in various colors and designs. Sometimes having a laser engraved design for aesthetic purposes.
There are shaped CDs that are business card sized that also fit.
If made of aluminum, it may provide RFID shielding for proximity cards.