My trouble. In my haste I checked where in the description it says that the side brushes are not compatible with the 645 and 655 models. For the 655, get the 800/900 robotic side brushes. I can't comment on the 645 model, but the following might help. If your Roomba has a gray brush side mount, you will need the same brush as the 800/900 series. You can confirm this on the i-Robot website. No stars because the seller mentioned incompatibilities and the products seem to be of decent quality. If Roomba has a blue brush side mount, you will need 500/600/700 series brushes.