Needle and chisel scalers use lighter percussive action than air hammers to rapidly and repeatedly strike a bundle of needles or a chisel against surfaces to clean off coatings and buildup. They are commonly used to remove rust, paint, dirt, and welding slag from metal surfaces. Scaler needles are metal rods that are held by the bundle in the barrel of a compatible needle scaler. They are loosely bundled, so they move independently to follow curves and contours. Scaler chisels are held singly in the barrel of a compatible needle scaler. They have a cutting edge or point and are more effective than needles at scraping, chipping, and breaking through heavy deposits.