Beryllium copper, also called beryllium bronze or spring copper, is one of the strongest copper-based alloys now available on the market. It has the highest strength of any copper-based alloy currently available. The commercial grades range in beryllium content from 0.4 to 2.0 percent. Because of the low beryllium to copper ratio, a family of copper alloys with unmatched strength comparable to alloy steel has been developed. The first of two beryllium copper families combines high strength with low conductivity, while the second family combines high conductivity with high strength. As a result, beryllium copper is available in two different families. In terms of fundamental features, these alloys stand out for their outstanding reaction to precipitation-hardening treatments, resistance to stress relaxation, and superior thermal conductivity.