The steel round shim has an unpolished (mill) surface and a standard tolerance. Steel provides good strength. It is magnetic. Shims are thin pieces of material placed between objects for a variety of uses, including added support, improved leveling, increased insulation, tighter seals, or better spacing. They also can be used to fill gaps between machine parts that are prone to wear. Shapes include round, notched, and slotted. Corrosion resistance describes the material"s ability to prevent deterioration caused by atmosphere, moisture, or other medium. Wear resistance indicates the ability to prevent surface damage caused by contact with other surfaces. Hardness (commonly measured as indentation hardness) describes its resistance to permanent surface deformation.