The plastic block of this brush actually measures 18" in diameter to fit up and underneath the apron of your 20" floor buffer. As the buffer starts to turn the brush, and weight is placed down on it from the machine, the bristles will splay outwards and scrub a 20" path.
For a more economical option, please take a look at the (wears faster than nylon), or for a much aggressive option, please feel free to take a look at the that we also have a vailable.