Screen-Bak Durite Q421 SC medium grit screen edger discs are more durable than paper or cloth discs and make a great choice for edge-sanding applications on concrete and hardwoods. Crafted with a sharp, P-grade silicon carbide grain abrasive, these discs deliver highly efficient cutting with minimal loading. The open-weave screen design ensures maximum resistance to loading when removing scale, rust and corrosion. These discs are waterproof, so rinse and reuse them to save money and eliminate waste.