This block is a combination of a brush to clean grout, and a pad driver to clean surfaces. This combined scrubbing action resaults in superior results when compared to standard rotary brushes and pad drivers. This reduces the need for multiple passes and is ideal for concrete, terrazzo, tile, and linoleum. Flexible enough for cleaning narrow grout lines and uneven surfaces. Accepts 13" cleaning pads. The secret of this grout brush to clean grout is; every second row of bristle were pulled out its socket. Anther words, it was thinned out. Hence the bristles can get into the grout to clean it because they are not densely stitched together. If they were, they would just glide on top of the tile and missing the grout. While the bristles doing their job on the grout, the floor pad is cleaning the tile surface. It is an excellent combination of two items. These brushes come in different sizes, we stock the largest one, the 17 inch diameter