it's the Ortleib back roller classic, top o the range, all over google, supposed to fit any rack, there's a kinda bar at the bottom that slides behind almost any part of the rack and two automatic clips on top that snap to the top bar, all very very adjustable, everyone loves them, me included, big inside, nice pocket for papers etc, totally waterproof, rock solid on the bike
pricey is the only problem, spec if you have to buy two when you want one ...
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