3/8"-24 13/16". XX-LARGE 64-65cm, 8-8 1/8 hat, 25 3/16"-25 5/8". XXX-LARGE 66-67cm, 8 1/4-8 3/8 hat, 26-26 3/8". XXXX-LARGE 68-69cm, 8 1/2-8 5/8 hat, 26 3/4-27 1/8". No helmet can protect the wearer against all possible or foreseeable impacts. A helmet can only protect the portion of the head that is covered by the helmet. For maximum protection, the helmet must be fit well with the chinstrap securely fastened. Failure to follow these instructions, the instructions printed on the helmet, and those contained in the owners manual may result in the possibility of the helmet coming off during an accident - possibly resulting in a severe head injury or even death. While riding motorcycles, scooters, ATVs and snowmobiles is fun, it can also be a dangerous pastime. A...  (less)