Main Roller, Central Brush for iRobot Roomba Combo R1138 / R111840 Pack: 2 rollers Central roller to improve the cleaning of your home, replaces the old brushes. It is recommended to replace this accessory every 2 to 3 months to optimize the cleaning of the house according to the use. Note: The data are all measured manually, please allow an error of 1-3 cm due to differences in light and display, there may be color differences, please refer to the actual item received.