These magnum-sized thin boxes were an instant hit at our store.  The 522-Slit version is perfect for trout nymphs, small to medium dry flies and chironomids.  

These boxes are a highly efficient way to carry tons of flies.  Each box is 12-inches by 8.75-inches but just under 1-inch wide.  They are great for anglers fishing out of a boat when you can keep these boxes nicely filed into a tackle bag or for keeping your "master supply" of flies organized at home.

Molded from nearly indestructible ultra-clear plastic.

Dimensions - 12 x 8 3/4 x 1 inches