That's how I refer to it. That round, beer keg lookin' . . solid construction Nelson-Rigg black zippered bag. It's flown off a couple times, but it never really hurt it. It's got a rain jacket you can pull over it. During storms, it gets power washed from the rear wheel, but my shorts stay dry. It has zippers on the ends to expand 3-4" more if needed. It works.