How many medals do the displays hold?

Medals are all different sizes, so it depends on which ones you display. For "typical" medal sizes we have found that the 4.5 inch will hold 1 medal, 9 inch will hold 2, 18 inch will hold 4 and the 36 inch will hold 8.

Do all displays work on the shelf and on the wall? How do I hang it on the wall?

All displays can be used in either mode. There are keyhole features in the bottom of each display that let you hang them against the wall using nails or screws. We recommend marking the wall by using the flat panel as a guide (before assembling the end caps). Then drill and place your screws. Assemble the end caps (but leave the badges out) and look into the display to help place the holes over the screws. Once secure on the wall push the badges into the end caps.

Are all badges interchangeable? 

Yes! You can put any badge into any end cap. Its a great way to upgrade or change your display. Also a great gift to buy someone who already has a display.