These brushes are 13" inches in diameter and fit our Viper Fang 26T automatic floor scrubber. 2 are required for the machine to scrub any floor. The bristles are a medium duty, for scrubbing any type of tiled floor. Our auto scrubber brushes are great for cleaning the high and low parts of any uneven floor. Take a look at our auto scrubbing procedures for more hints and tips on how to properly scrub your floor.