We have done our best to create a hole shape and size that will accommodate most bottle caps. This design is patent pending. There may be caps out there that will be too large or too small, and we apologize if that is the case. Caps that seem too large are often the result of bending during removal from the bottle and a little straightening out by hand will do the trick. Caps that are too small may require a little bending or even a small dab of super glue to ensure you can display them.
To install into wooden maps, press the caps in from the back side to allow the caps to deform a bit and "stick" inside the holes.  This video demonstrates filling up a map.