Two mounting systems included: saddlemen's "versa-mount" under-seat yoke and harness, and an adjustable sissy bar strap system that easily attaches bag to your motorcycle's seat, luggage rack or sissy bar. Backrest pad can be adjusted for additional comfort for the passenger or driver. Include Detachable backpack straps for easy off-the-bike jaunts. Include another large top-loading main compartment with internal organizer pocket. Five external pockets, two of which can be expanded for added capacity. Five internal and two outer mesh pockets. Rain cover with security tether protects the bag from the elements. Top exterior flap can be adjusted to carry a jacket. Mini-padlock, with extra keys, helps secure your belongings in the bag. Internal structure maintains bag shape and is strong enough to lean on, even when empty. br18 measures 11" w x 15" H x 1" D; 1,8 cubic inches cargo capacity; holds one 3/4 helmet plus other cargo. br34 measures 14" w x 19" H x 12" D; 3,4 cubic inches cargo capacity; holds one full-face helmet plus other cargo. No sissy bar required.