These 4-1/2" x 5/8-11" 40X Trim Back Flap Discs (70961) from Sait are designed for surface preparation, cleaning, and finishing applications on aluminum, stainless, and metal materials. They feature specially designed trimmable ABS plastic that allows you to easily trim away the back of the disc to expose more abrasive material, extending the life of the wheel. The abrasive material is a premium zirconium grain on a durable polyester cotton backing and is heat and strip resistant.