This is a key-chain design that exactly fits a 1 Euro coin. Just in case you desperately need a coffee and ran out of change, or to get a shopping cart!
To support my work, and help me make more free stuff you can buy something in my Etsy shop: http://www.etsy.com/shop/macouno
Print it without support to get a nice smooth surface on the bottom. Just detach from your platform with some pliers if it's stuck.
You should be able to stick in a euro with just a little force, and remove it just the same.