Above: Gold plated stainless surgical instruments.

Gold

MIL-G-45204
Type I 99.7 % gold minimum; hardness grade A, B, or C. Gold plating used for general-purpose, high-reliability electrical contacts, solderability, and wire wrap connections.
Type II 99.0 % gold minimum; hardness grade B, C, or D. A general-purpose, wear-resistant gold. It will not withstand high-temperature applications because the hardening agents in the gold plating will oxidize.

Type III 99.9 % gold minimum; hardness grade A only. Gold plating for semiconductor components, nuclear engineering, thermo-compression bonding, and high-temperature application.

Gold is a precious metal, which means that it will not oxidize in air, so its electrical conductivity stays uniform over long periods of time. Gold plating offers excellent corrosion resistance, good solderability, and when alloyed with cobalt, has very good wear resistance. Gold is commonly used in electrical switch contacts, connector pins and barrels, and other applications where intermittent electrical contact occurs.