The Norton A290 WallSand aluminum-oxide coated 9" abrasive disc has a hook-and-loop mounting system for quick disc changes on the Porter Cable 7800 drywall sander. Abrasive discs with hook-and-loop attachments don't require mounting tools, don't lose adhesion, and stay tightly attached to the sander for quick and easy grit changes during the project. The aluminum oxide grit is one of the most common choices for sanding drywall compound to a finish and is more durable than silicon carbide grit. The abrasive has been treated with a water-based zinc stearate coating that prevents clogs from forming and can be used in wet sanding applications. The disc has an open coat, which resists clogging and promotes flexibility. Open coat abrasives produce a rougher finish when abrading difficult-to-sand materials because the abrasive grains are spaced farther apart than they are on a closed coat product. The paper backing conforms to contours and delivers a more consistent finish than fiber or cloth backings. The backing is made from A-weight paper, which is the lightest and most flexible of the paper backing options for maximum conformability. Recommended Grit Sizes P150 grit (very fine) For light sanding or sanding the final coat of drywall compound P120 or P100 grit (medium)For sanding the second coat of drywall compoundP80 grit (coarse)For sanding the first coat of drywall compoundCoated abrasives have individual abrasive grains spaced at a predetermined distance from one another. They are used for a variety of applications — from shaping a part to fine finishing, depending on grit size. Low grit numbers such as 40 are coarse and are used for removing excess material and shaping a part. High grit numbers such as 400 are rated as fine and help create a smooth surface finish. Closed coat abrasives are 100 percent covered with abrasive grains, which extends the abrasive's life, maximizes material removal, and achieves finer finishes on metals and hard materials than an open coat. Closed coats are only recommended for use with non-clogging materials. For open coat abrasives, 50 to 75 percent of the surface is evenly covered, which provides a rougher finish because the abrasive grains are spaced farther apart than on a fully coated product. The gritless spaces promote flexibility and resist clogging when abrading difficult-to-sand materials. The flexibility or rigidity of the abrasive product is also affected by the choice of backing material (either paper, cloth, or fiber). Paper backing, the most flexible backing option, contours to the workpiece and delivers a more consistent finish than fiber or cloth backings. Paper backings are categorized by weight from lightest to heaviest (A- to F-weight respectively). Cloth backings are slightly more rigid, durable, and tear resistant than paper backing, but can still withstand repeated flexing. Cloth backing is categorized by weight from lightest to heaviest (J-, X-, Y-, and H-weight respectively). Fiber backing is the strongest and most rigid backing option, and is recommended for aggressive material removal. Norton Abrasives manufactures sanding, grinding, and polishing abrasives. The company, founded in 1885, meets International Organization for Standardization (ISO) standards 9000 and 14001 for quality and environmental management.