This is one of a big bunch of “holders” (pockets/wallets/folders) designed to fit the 4" x 4" Coasters announced with the Coins, Coasters & Holders Kit.
This particular one is scored chipboard to make a FAT folder (with a deep pocket that can hold up to 3 coasters, depending how heavily you embellish them). When folded closed it measures approx. 4-1/2" x 4-1/2".
Note that the covers overlap (they don't meet in the middle when folded closed). You could add a "button and string" closure to tie the folder closed (just an idea).
There are lots of extra photos above, including one showing one of these folders with the smaller 3 Inch Dimensional Coin Folder.GND 190428new 190523EM