Ortlieb says about the Back-Roller Classic QL 2.1
A pair of rear panniers with roll closure and the Quick-Lock 2.1 system: PVC-coated polyester fabric: inner pocket: large reflectors: shoulder strap. Compatible with racks with 16 mm tubing. 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).