Nice magnet for bottle cap display: round ceramic magnet with a diameter of 3/4 inch and a quarter inch thick. Not available at your local hobby store: ours are thicker!
Turns any bottle cap (raw or used) into a great fridge decoration or collectible, with no need for glue, since crown caps are steel and thus magnetic. Most surfaces are more magnetic than a bottle cap, though, so if you want them to stay together, a spot of hot glue or super glue will be needed.
The magnet is thick enough that it protrudes some on a raw cap and a little on a traditional used cap, so the cap edges don't come in contact with your fridge.
One magnet ships for the rate of 5 bottle caps. Magnets ship next to the caps; you assemble as desired. Priced per magnet, caps not included.