Flexible rubber construction: the block is made from heavy-duty, flexible rubber, designed to securly hold sandpaper in place, ensuring consistent and effective sanding across different materials. Holds paper securely on bottom for flat sanding or on top for tackling curves. Fits 1/4 sheet of standard 9" x 11" sandpaper. The block is designed to fit 1/4 sheet of standard sandpaper, making it easy to load and use with your perferred grit of sandpaper.