Flexible disc and is perfect for removing paint & rust from flat or contoured surfaces. Ideal for sanding on many surfaces, including wood, metal, and fiberglass. Will not discolor your sanding surface. Sanding should be done in a sequence, going from coarse to fine, skipping no more than one grit level. Fits all standard household drills: 1/4 inch, 3/8 inch and 1/2 inch.