If you are looking for an approved helmet with smallest possible shape - look no further. The Bandit Slimline has a compact shell design but still meets all ECE R22-05 safety requirements. It features a detachable sun visor, comfortable velours lining, a padded quick-release chin strap and three snap studs. In order to keep outer dimensions as small as possible Bandit works with three shell sizes:

small - for helmet sizes XS to M1

medium - for helmet sizes M2 to L

large - - for helmet sizes XL to XXL

That explains the unusual size M separation into M1 (57) and M2 (58).