Grey blue; synthetic corundum = 10 A Type 1, straight, for various bench grinders. Tool grinding machines and other stationary grinders. Field of Application: For general workshop requirements, for sanding steel, iron, wrought iron etc. of standard hardness. Advice: Plastic adapter sleeves for reducing 32 to 25, 32 to 20, 32 to 18, 32 to 16 are included in all sanding disc packs.