1.For roomba series, 500 600 700 800 900. Easy to clean. 2.Please notice the difference between E series and this one.The metal needle of this one is flat and the E-series metal needle is pointed.We also sell the E-series l wheel，please look inside the shop. 3.This product is to pass the metal rod through the ball, and then force into the plastic frame. If it falls off, please install it as described above.