If you want to mount the pannier on the rack permanently you can unbolt the rack and then slip the leg of the rack through the webbing strap on the back of the pannier then re-bolt the rack to the bike. Pannier is now "locked" on the bike. Not what you want to do if you are removing the pannier all the time. Myself, i used to leave an old pannier permanently attached to my bike like that and then stuffed by shoulder bag into the pannier when commuting. So I always had a clean dry shoulder bag to carry around at my destination.