Ortlieb says about the Handlebar-Pack 15 L
Waterproof handlebar bag: roll closure on both sides for optimal access: spacers for attaching to various types of handlebars: Velcro straps for attachment: valve and loop for compressing the pack volume: hooks for attaching the optional accessory pack: suitable for mounting on carbon handlebars.
Version 9 L: Ideal for mounting on road bike handlebars
Version 15 L: elastic cord on the outside to fix equipment