Ortlieb says about the Sport-Roller Classic QL2.1
A pair of universal panniers with roll closure for lowrider or rear rack (e.g. for children's bikes): Quick-Lock2.1 system for luggage racks with up to 16mm in tubing diameter: PVC-coated polyester fabric: including inner pocket: reflectors: shoulder strap: can be combined with rack pack 24 L and 31 L on the rear rack.
Accessories available separately: Carrying System Bike Pannier: Anti-theft device (E124): Outer pocket 1.8 L: Mesh pocket: Bottle cage: QL2.1 hook 18 mm (E211) & 20 mm (E193).