1. History

In the early 1930s, Cannon (now ITT Interconnect Solutions) was contracted by Douglas Aircraft Company to develop connectors for use on the DC-1 and on the subsequent DC-2 and DC-3 aircraft platforms. During the late 1930s—with World War II on the horizon—Cannon began volume production of multi-contact electrical connectors that were used by virtually every aircraft builder in the United States . Cannon's Type "AN" (Army/Navy) series of connectors set the standard for modern military circular connector specifications now specified under the MIL-C-5015/MIL-DTL-5015 military specification.

2. Circular Connector Terms and Definitions

The following Connector Terms and Definitions apply to circular connectors.^[1]

Accessories or Backshells are mechanical devices (e.g., strain reliefs, cable clamps, adapters, potting boots) that are threaded onto the rear connector accessory threads of plug or receptacle connectors to make up the total connector assembly.

Bayonet Mount interconnect mating designs use pins on the receptacle and ramps on the plug for quick-connect and disconnect coupling. Reverse Bayonet puts the pins on the plug and ramps on the receptacle.

Contact refers to the conductive element in a connector that mate mechanically and electrically to transmit signals and/or power across a connector interface. Crimp style contacts are the most common type found in high-reliability cylindrical connectors. Male contacts are sometimes referred to as leads, posts or pins, while Female contacts are universally known as sockets.

Contact Arrangement or Pattern is the gauge, number, spacing and arrangement of contacts in a connector. Contact arrangement selections are based on the current and voltage requirements of the application, and the space available for the connector package.

Contact Resistance is the measure of electrical resistance across a pair of fully mated contacts. Measured in ohms or millivolt drop at a specified current, contact resistance is affected by normal force (i.e., the static force on the contact interface), plating quality and the physical geometry of the contact.

Contact Retainer is a locking clip or tang used to secure a crimp contact in place within the connector insert. Contact retention specifications define the force required to remove a properly seated contact for each class of connector.

Contact Retention is the pressure a contact can withstand, in either direction, without being dislodged from the retaining clip which holds it within the connector.

Contact Size is an assigned number denoting the outside diameter of the engaging end of the pin contact. The larger the number, the smaller the size.

Contact Spacing or pitch is the distance—center-to-center—between adjacent contacts.

Coupling Ring is an accessory feature of the connector plug which aids in mating and unmating plugs and receptacles and prevents decoupling of the connector.

Crimp refers to the physical compression (deformation) of a contact barrel around a conductor used to make an electrical connection.

Crimp Contact is a connector pin or socket whose back portion (wire barrel) is a hollow cylinder into which a stripped wire (conductor) is inserted. The sidewalls of the wire barrel are then mechanically compressed (uniformly deformed) using a crimping tool to captivate the conductor..

Dielectric refers to a material having electrical insulating properties (e.g., a contact insulator in a connector or the jacketing on a wire).

Electrical Connector is a separable device that provides mechanical and electrical contact between two elements of an electronic system without unacceptable signal distortion or power loss.

Environmentally Sealed connectors and backshells are designed to prevent fluids, moisture, air or dust from degrading the performance of electrical contacts and conductors. "Environmental" components typically use gaskets, grommets, potting materials or interfacial and O-ring seals to prevent the penetration of foreign substances into the body of the part.

Flange is an integral mounting plate on some bulkhead and feed-through connectors used to attach the connector to the chassis or panel. The connector flange is typically square, and is mounted to the panel with threaded screws.

Hermetic vs. Water-Proof vs. Water-Resistant refers to the coupling seal between the contacts, connector insert and body. A true hermetic connector provides an airtight seal and can support and maintain positive pressure or a vacuum. Waterproof connectors prevent liquid ingress when immersed using a variety of methods (e.g., molding, potting and encapsulating) to prevent water intrusion at high hydrostatic pressures. Water resistant implies that a coupled connector will prevent water ingress that can lead to shorting in shallow standing water or rain. Typically this is achieved by inserting rubber gaskets and compression seals at the contract region as well as at the cable entry.

Hyperboloid Contact^[2] - To deliver ensured signal stability in extreme environments without reliance on connector packaging protection it is necessary to move away from the traditional pin and socket design. The Hyperboloid Contact is specifically designed to withstand the most extreme physical demands. The female contact has several equally spaced longitudinal wires twisted into a hyperbolic shape. As the male pin is inserted axial wires in the socket half are deflected wrapping themselves around the pin providing a number of contacts paths.

Insert is a molded piece of dielectric material that fits inside the connector shell and supports the connector contacts. Inserts are tooled for each shell size, and contact arrangement. Inserts made from resilient materials also contribute to environmental properties.

Interfacial Seal is an elastomeric seal for mated connectors and their individual contacts. "Cork & bottle" seals feature a raised shoulder around each pin contact that compresses into a corresponding hole on the socket contact insulator.

Plug refers to the half of a connector pair designed to attach to a wire or cable; as opposed to the Receptacle half which is typically mounted to a bulkhead, panel or box. Even though plugs are usually thought of having male (pin) contacts, they can in fact house any type of contact—pins, sockets or even both. Therefore, it is the design and location of the connector which makes it a plug, not the gender of its contacts.

Polarization refers to design features on mating connectors—such as keyways or shell geometries—to insure connectors can be mated in only one possible orientation. Often a key or dog use a short pin that slides into a corresponding slot or keyway is used to guide the plug and receptacle together during mating to insure polarization of the mating contacts. Guide pins can also be used to insure correct polarization.

Rear Release or Crimp and poke style contacts may be removed from the connector for maintenance using a special hand-held tool. In rear release designs, the tool is inserted into the rear (cable side) of the connector to disengage the contact from its retaining clip. The disengaged contact is then removed from the connector by lightly pulling on the attached wire.

Receptacle refers to the other half of the connector pair, designed to be mounted—with jam nut fittings or other fastener hardware—to a bulkhead, panel or box. Inline receptacles are also available for cable-to-cable connections. As with the plug, it is the design and location of the receptacle in the system, not the gender of its contacts, which makes it a receptacle.

Scoop Proof describe a longer shell design on the pin half (plug or receptacle) of a connector. The longer shell allows the pin contacts—protruding from the face of the connector—to be recessed sufficiently so as not to be damaged if the mating shell is "scooped" into it during mating process. This prevents pins from being bent or contacts from being electrically shorted during mating.

Solder Contact is a pin or socket contact that accepts a conductor (wire) which is soldered onto the "solder cup," not crimped into the wire barrel.

Threaded Coupling interconnect mating designs use a threaded nut on the plug, and a corresponding set of threads on the receptacle, to mate the pair of components. The coupling nut is usually equipped with flats or knurling for easy assembly. Different thread types, profiles and geometries provide different functionality. Buttress Threads, for example, are often specified on plastic connectors due to their enhanced tensile strength. The MIL-C-38999 connector incorporates a triple-start threaded coupling mechanism for greater vibration protection and faster mating and unmating.