This listing is for an 18″ diameter nylon brush, to properly fit into a 20″ floor buffer. Measure the space inside the buffer skirt, ad choose a block diameter that will fit inside that, it you measure 18 1/4″, then this 18″ block is the perfect fit for your 20″ model floormachine.Nylon brushes are a great choice for scrubbing jobs, whether it be hard flooring, or carpeting. Generally, we recommend soft “KARPET KARE” (or “KK” for short) for carpeting jobs. The “KK” brushes are a blend of soft white nylon in the inner rows, with medium black bristle around the edge. This allows the brush to be run on carpet without having it dig into the carpet, which usually causes blown fuses or circuit breakers. Solid black bristle can be run on carpeting, but you may need to break the brush in by running it on wet concrete for anywhere from 10-30 minutes. You’ll know when the brush is broken in, as the bristle will take a slight “set” in one direction. Run your hand across the bottom of the bristle, it’ll slide in one direction, and get caught in the other, your brush is now broken in. Simply measure inside diameter of your buffer skirt and order the diameter that will fit inside of that.