Lead increases the machinability of brass as well as increasing its strength and resistance to corrosion. The addition of lead also seals shrinkage pores to provide pressure tightness. Brasses can contain up to 3.5 percent in lead contents, and are classified as low, medium, or high-leaded. Leaded brass may be used to make screws, valves, fittings, bearings, specialty fasteners, architectural hardware, and general purpose machine parts.