The slot is through the front and back of the holder to “lock in” the card Standard Prox Card Holders are made with soft, flexible .020” thick material front and back to prevent tearing. Heavy-Duty Proximity Card Holders available with .020” thick front and .030” thick back to handle even thicker card or multiple cards without splitting. Made in the United States of AmericaThis item is made and stocked in Chino, CA.