Military (MIL-SPEC) connectors are shell-type connectors which are built in accordance with military specifications. Their design takes into account the need to protect the connection from environmental factors, allowing them to be used in military and aerospace applications. The type AN (Army-Navy) connector set the standard for modern day connectors. They are often referred to as Military Standard, "MIL - STD", or "MIL - SPEC" connectors.

Connectors typically consist of a mating pair, known as a plug and receptacle, and each pair is equipped with male (pin) or female (socket) contacts. Connectors used for electrical connections are typically made of beryllium copper or phosphor-bronze which is then plated with gold or some other type of non- corrosive, highly-conductive metal. Connectors used for fiber optic connections are typically plug (male) connectors with a protruding ferrule that holds the fibers and aligns two fibers for mating. An important specification for fiber optic connectors is the insertion loss, which is the amount of light lost in the connection.

Specifications

Selecting military (MIL-SPEC) connectors requires an understanding of product parameters. Parameters to consider when specifying military (MIL-SPEC) connectors include:

Number of contacts - The number of contacts is the number of conductive elements in a military connector which mate with a corresponding element to provide an electrical path.

Contact type - Contact types can be either pins or sockets.

Coupling type- Coupling types can be bayonet, threaded, push or pull (ball detent), breech lock, and spring rack or quick connect.

Contact size (American Wire Gauge - AWG) - Contact size is the designation used to differentiate one contact from another, typically denoted using AWG.

Shell Specifications

Shell size- The most common shell sizes are available in .0625" increments starting at shell size 8 (.50) to shell size 36 (2.25). Both the connector and accessory manufacturers use the term "size" to designate the size of their respective products. Military (MIL-SPEC) connectors, which use threads to attach backshells, are usually equal to or within .062 of the connector shell size.

Shell style - The main connector housing is called the shell. For circular military (MIL-SPEC) connectors, the shell is cylindrical and available in incremental sizes starting around .375" in diameter. The shell style or gender can be straight plug, angled plug, wall or box mount receptacle, in line or cable receptacle, dummy receptacle, solder or weld mount receptacle, jam nut receptacle, and thru-bulkhead receptacle.

Shell gender- The gender is noted as male or female. Male "plugs" are also called header or free connectors. The plug is normal the movable portion and is attached to a cable of removable sub-assembly. In shell-type multiple contact connectors, the plug usually contains the socket contacts and is mounted on the "hot" (rack) side of the system. Plugs are inserted into female connectors such as receptacles, jacks, outlets, etc. to make circuit connectors. 

Terminals

Terminals are devices that terminate a connection. They attach to posts, studs, or other conductors in order to establish an electrical connection. There are several options including,

Cage clamp- Electrical connections are made using a cage clamp.

Crimp- Crimp is the physical compression (deformation) of a contact wire barrel around a conductor to make an electrical and mechanical connection to the conductor.

Crimp. Image Credit: Multi-Contact

Insulation displacement connectors (ICD) - IDCs slice through cable insulation to make a connection. Forcing an insulated conductor into a restrictive slot in the connection part of the contact displaces the insulation so that the bare wire engages the sides of the slot. IDCs are mass termination connectors for flat cables and eliminate the need to strip insulation.

PCB solder- Electrical connection is made by soldering wires onto a printed circuit board (PCB).

Screw- Electrical connections are made using screws.

Lugs- Electrical connections are made using lugs.

Lanyard release- The lanyards can be of various lengths. Compliance with specific MIL-SPEC standards, the inclusion of backshell accessories and a lanyard, and applicability to audio or visual applications are other important considerations

Solder cup or solder- Solder cups are terminal ends or contacts into which conductors are inserted before soldering. A metal or metallic alloy is used to join metal surfaces together. Normally, a 60-40 rosin core (60% tin and 40% lead) is used for soldering electronic assemblies. Soldering is a wet process.

Tabs- Electrical connections are made through quick connect tabs.

Through-hole technology (THT)- THT mounts components on printed circuit boards by inserting component leads through holes in the board and then soldering. In pin termination, components are mounted on PCBs without soldering.

Wire wrap- Electrical connections are made by wrapping a stripped or unstripped solid wire around a terminal post that contains a series of sharp edges. This solderless process requires a special wrapping tool.

Military Specifications

Specific military specifications that can be met by military (MIL-SPEC) connectors include:

Other standards for Military (MIL-SPEC) connectors include RoHS compliance and ARINC.

RoHS Compliant- Restriction of Hazardous Substances (RoHS) is a European Union (EU) directive that requires all manufacturers of electronic and electrical equipment sold in Europe to demonstrate that their products contain only minimal levels of the following hazardous substances: lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyl, and polybrominated diphenyl ether.

ARINC - ARINC is a technical standard for the avionic industry. An ARINC connector complies with this standard and is used to interface avionic equipment.

Coupling Type

When selecting a military connector it is important to consider the type of coupling needed for the application. A coupler is a connector used to facilitate the joining of elements. It is typically associated with the transference of power or transference of electric waves, from one device or component, to another.

Features

Military (MIL - SPEC) connectors are available with additional features that help it perform in the desired application.

Integrated filter/magnetics- The connector has a filter to protect it against unwanted signals or magnetics to provide filtering, signal conditioning or isolation.

Underwater use - The connector has the appropriate sealing so that it can be used in underwater applications.

Hermetically sealed - The connector is hermetically sealed, allowing no internal moisture leakage.

EMI or RFI filter/ ESD shield - The connector has a filter to eliminate electromagnetic interference (EMI), radio frequency interference (RFI), and/or shielding to prevent electrostatic discharge (ESD) or EMI.  

Environment resistant - The connectors are able to withstand various environmental challenges including chemicals, sun, dirt, etc.

Images credit:

ICC