Ortlieb says about the Back-Roller High Visibility Single
Rear pannier (single bag) with roll closure and Quick-Lock 2.1 system for racks with up to 16 mm diameter tube. Features PU-coated fabric with incorporated reflective thread: an inner pocket: large reflectors and shoulder strap. Can be combined with rack pack 24 L and 31 L on the rear rack.
Accessories available separately: Packing Cubes / Commuter Insert for Panniers: Carrying System Bike Pannier: Anti-theft device (E125): Outer pocket 1.8 L: Mesh pocket: Bottle cage: QL2.1 hook 18 mm (E211) & 20 mm (E193).