Nintendo Enamel Pin
Backings: 2 Metal Backings
Enamel: Soft Enamel
Also available as a limited pin set with Playstation and Sega pins here.
Standard backings are either Rubber or Metal Butterfly backings. These will securely hold your pin on, but locking backings are almost guaranteed to keep your pin in place. Think of them as 'pinsurance' for your most prized pins.