The RJ45 Modular Connectors & Modular Plugs are the main connection between devices. There must be a type of metal to accomplish and maintain a stable conductivity. Gold is the perfect solution since it does not corrode and very durable. Others metals such as copper and nickel will degrade and lose connection over time when exposed to the outside elements like humidity and moisture. The amount of gold plating that can be placed on connectors is measured in microns. 50 microns is the thickest gold plating available, which is great for maintaining a fast and stable connection and can deliver up to four times as much throughout. FCC and IEC specifications call for a minimum amount of gold or nickel to be used in RJ45 plugs, but a recent study found that more than 50% of tested plugs did not meet this minimum. Because there are a large amount of inferior Ethernet cables on the market, it is important to look for those that specifically say that they have 50 microns of gold plating. FCC and IEC specifications also require connectors that are at least 99% pure gold and have no surface defects.
If cable manufacturers advertise their plugs and connectors have 50-micron gold plating then most likely they are using 99% pure gold.