Flutter Blade Bicycle Noise Maker (Flag and Butterfly 2 Pack) Clip onto the fork or frame of your bike and take off - it's that easy to Rev Up the Fun! Kids ages 4 and up love the engine-like sound Easy to install and adjust the volume - only 2 pieces Made from high-quality, ultra-durable material for long life. Great gift for birthdays, holidays, and any time you want to Rev Up the Fun!