Note that the rolling ball only protrudes slightly from its plastic mount - they don't work on carpet at all. Not all of the reels in my 8-pack rolled smoothly prior to attachment and tended to "hang" in position or wobble when rolled with just one finger. It's possible that some of the ones I used were defective and 'frozen', at least in part because I noticed they left scratches/marks on my bathroom tile - unlike plastic casters, metal is harder than most flooring materials and can damage/scratch wood or tile floors if you walk over the same area multiple times. After using this issue a few times on bathroom tiles I removed them and have no plans to use them again.