[392cobra]

There are two different Snell ratings.
M - Motorcyle
SA - Sports Application

Snell "SA" (Sports Application) rated professional helmets are designed for auto racing and provide extreme impact resistance and higher fire protection.

Key differences between SA and M Rated Helmets (from Snell website):
SA standard requires flammability test while the M standard does not.
SA standard has rollbar impact test while M standard does not.
SA standard allows narrower visual field than M standard (Some SA helmets aren't street legal).

Don't cheap out an get an motorcyle helmet.Get something worthy of your life and Cobra.
Go to a Track Day with the wrong helmet and they will send you home.