Semi-metallic – primarily contain steel fiber and iron powder(＞30%), abrasives and lubricants.
 

Low-metallic – contain some steel fiber and/or iron powder(＜30%), various abrasives and lubricants, some non-ferrous metals. 
 

Non-asbestos organics (NAO) – contain nonferrous metals, various abrasives and lubricants, mineral fibers and other reinforcements.