I read a review mentioning the poor tolerance of the rail.
When I saw the Pletscher three point Easy Fix system that was the same as most good scooter and motorcycle top box mounts, it was clearly the better design.
This picture just illustrates it better than words.
But here’s some more words with the picture, while I appreciate my lovely Pletscher Easy Fix system!
The bag would not slide on an off easily anymore and it soo loose that it had a slop left and right. The bag eventually got so loose that every time I’d hit a bump I’d hear the bag lift off and slap the rack hard. It was like a sledge hammer pounding on the rack every time I hit a bump or pothole. The vertical strut member on the rack finally cracked and I ended up replacing the rack with a stronger one made by Zefal that was rated to 50 pounds. Then I eventually drilled 2 holes at the bottom of the bag and bolted it permanently to the deck of the new rack.