+1I have the SW-Motech Pro Tank Ring, it works well.
Givi also has something similar called TankLock:
Givi Tanklock Tank Bag Mounting Flange
Purchase the Givi Tanklock Tank Bag Mounting Flange at Canada's Motorcycle. Free shipping and Easy returns.fortnine.ca
I’ve had a few sw-motech ones and Givi ones that mount on a tank ring and both are good. Givi is less expensive and will do the job just fine, but it certainly feels cheaper and my zipper broke on one bag on a long trip. Buy once, cry once.
Don’t think my newer sw-motech will ever break as it’s really well built. I like that it’s also got the magnetic ring for easier time getting it on. It’s also adjustable so it can slide slightly forward or back to better suit various riding positions or tank profiles.