The best bang for the buck is polypropylene bristle. This is a synthetic fiber with a low cost, and great scrubbing action.
Prices included the standard NP-9200 clutchplate already mounted for you.
Please note that the price list shows actual block diameter .For this type of brush we suggest it fit inside the skirt of your floor machine. Simply measure inside the skirt and order the whole inch diameter that will fit inside the skirt ( ie you measure 15 1/4" inside your machine, then a 15" block would be a correct fit).