Sparkling shamrocks ride on a snap-on band that fits adults and older kids alike, secure enough to survive a parade without constant adjusting. It weighs next to nothing, so it stays comfortable for the whole event, and the build takes repeated wear: this is a bin-it-for-next-year accessory, not a one-day one.
Sold by the package (1 headband) or by the case (6 headbands).