The 2.5x2.5 coin holders are 2.5" x 2.5" in size then they are holding a coin. All you need to do to use them is place a coin on the window, fold the hold over and staple shut. These cardboard coin holders are made with tough mylar windows designed last for years. Mylar windows are perfect for storing coins because they will not tear or allow dust and moisture to penetrate the holder and damage the coin.
The 1.75" window, or 44.45mm, will hold larger diameter coins the 2x2s can be too small to hold. These include Silver Dollars, Silver Rounds, Medallions, and Casino Chips. Collectors also like to store Silver Dollars in these holders because there is extra space on the holder to write notes about the coin.