The Carlisle 4042514 Spectrum Boot 'N Shoe brush replacement with blue bristles works with a Carlisle 4042403 brush (sold separately) to help remove bacteria, refuse, dirt, and other contaminants from boots and shoes before entering sensitive sites, such as food processing areas. The bristles are made of polypropylene for durability and extended life. The base resins used for the bristles are U.S. Food and Drug Administration (FDA) approved. The brush is free of BPA (Bisphenol A) to address safety concerns raised by the U.S. FDA and other organizations. The block dimensions are 10 x 4-1/2 x 3-1/2 inches (L x W x H). (L is length, the horizontal distance from front to back; W is width, the horizontal distance from left to right; H is height, the vertical distance from the lowest to highest point.)