The "Bottle-Fly" Butterfly Knife Bottle Opener.This dual-purpose butterfly knife is a bottle opener and doubles as a butterfly knife trainer with its dull edges. So give this cool butterfly a try, and while you're practicing open up a bottle and celebrate your new knife skills. Perfect for the bartender in your life. Specifications: Overall: 8.75" Closed: 5.25" Weight: 4.9 oz.