The M12 family has many variations, and thus to minimize incorrect mating of similar looking connectors on a panel, they are coded so that only like-coded connectors actually mate. The most common is “A” code, which originally had four or five contacts. This has been extended to twelve, with eight contacts becoming a standard for industrial Ethernet at 1Gbps speeds. For common factory floor speeds of 10/100, the “D”’ code is used. In addition to the insulator coding, “D”’ code connector insulators are often colored green.