What Are MIL-SPEC Connectors?

At some point in an electrical or electronic engineering career, you might come across MIL-SPEC Connectors, also known as MS or Military Standard Connectors. These electrical or fibre optic circular shell connectors were originally developed by the military for tactical service and aeronautic applications in the 1930s, and were then called AN or Army/Navy connectors.

They're now a standard feature in military equipment and other severe or demanding environments, including marine, aerospace, oil and gas applications, and various industrial and automotive contexts. This type of electrical connector was specifically developed to protect the connection against the harshest possible environments, and is designed for durability. Depending on the application, connectors can be selected for resistance to corrosion, vibration, extremes of temperature, and more.

MIL-SPEC connectors are usually composed of a mating pair, one half of which is a plug and the other a receptacle. Each pair must match a male (pin) contact with a female (socket) contact. For making electrical connections, the connectors are commonly made of a phosphor-bronze or beryllium-copper alloy. This is then plated with some type of highly conductive and non-corrosive metal, such as gold.

For fibre optic connections, the connectors are usually male plug connectors that feature a protruding ferrule. This holds the fibres in place, and lines up the two fibres so that the connection can be made. An important specification to take into account when selecting fibre optic connectors is the insertion loss. This is a measurement in decibels (dB) of the amount of signal power or light that will be lost in making the connection.