Cliff Keen F5 Tornado Headgear - Boys' Grade School Keep your head in the match! New design based on NASA research. 43% lighter and remarkably cooler. Made from the strongest components to provide incredible durability. Combats bacterial build-up. Greater Audible Sound™ technology. PowerTab™ strapping system adds better, faster fit. Sz: Fits head circumference of 18-21.5".