Electrical or fiber-optic connectors used by U.S. Department of Defense were originally developed in the 1930s for severe aeronautical and tactical service applications, and the Type "AN" (Army-Navy) series set the standard for modern military circular connectors. These connectors, and their evolutionary derivatives, are often called Military Standard, "MIL-STD", or (informally) "MIL-SPEC" or sometimes "MS" connectors. They are now used in aerospace, industrial, marine, and even automotive commercial applications.
Characteristics Connectors usually consist of (i) a mating pair (plug and receptacle) each equipped with male (pin) or female (socket) contacts; note that at least one of the connector halves, or its contacts, should be floating to minimize mechanical stresses.
Electrical connector contacts are typically beryllium copper (BeCu) or phosphor bronze which is then plated with gold or some other non-corrosive, highly-conductive metal. The contacts are contained by a dielectric insulator (typically a layered construct of various polymers or glass depending upon connector series and manufacturer, and often known as the insert) and are housed in an enclosure (i.e., shell), that is often aluminum and plated or anodized for corrosion protection. The contacts may be captive or removable using a special tool. The electrical connection into the system at the contact terminal is either a soldered or crimped connection. The seal between the shell and insert may be moisture resistant or a hermetic seal. The inserts in each connector half must be oriented for correct mating, and the shell or insert usually contains a keying feature to prevent mis-mating that could damage the connector or result in an electrical problem. Cable clamps and other mounting hardware may be provided, and the mated halves are usually secured by a locking mechanism to prevent disengagements. Fiber optic connectors are typically plugs or so-called male connectors with a protruding ferrule that holds the fibers and aligns two fibers for mating. They use a mating adapter to mate the two connectors that fits the securing mechanism of the connectors (bayonet, screw-on or snap-in.) A primary specification issue for fiber optic connectors is insertion loss, i.e., the amount of light lost in the connection expressed in dB.
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