All Little Nutty helmets comply with US CPSC Bicycle Helmet Safety Standards for persons age 5 and older. Little Nutty helmet is size XS, and fits heads 46cm - 52cm/18" - 20.5". See Little Nutty Size Chart to determine a good fit. If your head measurement is 52cm/20.5" (maximum size of Little Nutty XS), we recommend ordering a S-M Street helmet. Each Little Nutty helmet has a built-in Spin Dial Fit System to ensure a snug, comfortable fit, as well as a soft, fabric chin strap for comfort. For information on returns, see Nutcase Return Policy. This helmet has the Gen1 clasp buckle system.