Circular Connectors Information

Circular ConnectorCircular connectors are multi-pin connectors primarily used for external interfacing. They can be used for data transfer, electrical signal transmissions, or for powering electrical devices. In some cases circular connectors have been designed to carry what may be referred to as a mixed signal and may be described as a power and control connector. These types of multi-pin connectors are used for both power and signal transmissions.

Types of Circular Connectors

The term, circular connector, was originally exclusively used to specify a circular plastic connector (CPC). These types of connectors, or circular metal-shell connectors (CMC), are used in industrial applications where a robust and secure wire connection is needed. They are designed to withstand an abusive environment while offering a secure connection for industrial applications. Circular connectors may also be used to describe other types of connectors including DIN connectors, military connectors and micro or nano connectors.

Circular plastic connectors (CPC) and circular metal-shell connectors (CMC) are both designed by an OEM where the plug and receptacle are commonly configured to mate exclusively with their own connectors. The shell size, type of thread or coupling and contact arrangement disallow the insertion of connectors made for other applications or manufactured by other OEMs.

Military (MIL-SPEC) connectors 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.

DIN connectors are high frequency, multi-pin, electrical connectors that meet standards established by Deutsches Institut für Normung (DIN), a German national organization for standardization. The ends of DIN connectors are round, notched, and protected by a metal skirt to ensure that pins line up correctly.

Micro connectors and nano connectors exhibit contact pitches of 0.05" (micro) and 0.025" (nano), respectively. They have one or more rows of plated contacts and are either straight or right-angled.

Contacts, Insert and Shell Sizing

Circular connectors are defined by the number contacts, shell size and contact diameter. Each connector is proportionally sized for its application. Standard connectors are manufactured according to DIN or military standards. The connector will accept a range of contact sizes and may be offered with several different insert options. Some connectors are offered without inserts or contacts. These connectors function as a protective housing that can be customized for specific applications.


Circular connector design view. Image Credit: LAPP USA


The insert is an insulating body inside the shell. It is used to orientate the electrical connections. Each insert is designed to support given types or sizes of contacts. They have a contact arrangement which allows them to accommodate as many conductors as are available contact slots. When wiring the contacts it is not necessary to use every available contact slot. A six conductor cable that meets the cable diameter requirements may be used with an insert that can support more than six terminations. In some cases it is preferred to only occupy a portion of the available contact slots, so that the plug and receptacle can be oriented by aligning the blind or missing contacts.

Electrical Contacts

Electrical contacts are soft, high-conductivity, oxidation-resistant materials used as the makeup of electrical connections. The electrical current flows through this material.

Shell Sizing

The shell is commonly used to describe the size of the connector. The shell size is a nominal figure designated by a two digit number which is sometimes followed by a letter code. The two digit number is used to specify the number of 1/16th inch increments in the diameter of the shell.

Larger shell sizes are generally used to house larger contacts used for power. Inversely smaller shells are designed to house smaller contacts needed for sensors. Intermediate shell sizes are used to accommodate flexibility in contact size and arrangement. Each shell can also be used with a range of cable diameters. 

Selection Criteria

Important parameters to consider when specifying circular connectors include the connector type, gender, terminals options, mounting options and performance criteria.


A connector will either be male type (with pins) or female type (with sockets). A male connector includes pins that plug into a socket or similar receptacle. A female connector consists of sockets that are aligned to mesh with a pin-type connector.

Male plug. | Female receptacle. Image Credit: CONEC | LADD Industries, Inc.


Connector termination describes how the conductive elements mate with the electrical contacts in the connector. There are several types of terminal options. Termination options include insulation displacement, solder cup or solder, PCB solder, wire wrap, tabs, screws, lugs, and crimp.


Circular connectors may be designed to mount on a cable end, panel, circuit board or other entry point. There are several methods for affixing the connector including the use of bulkheads, jam nuts, flanges and inline cable mounts.


Voltage and Current Ratings

The maximum rated voltage or current describes the carrier signal that the connector is designed to accommodate. The voltage and current ratings are controlled by the size and type of contacts used. Low amperage and voltage ratings are associated with products used for sensors and electrical signals. The load required to power a device is generally significantly larger than other transmissions and power connectors are associated with higher voltage and current ratings.

  • Current describes the current (rate of flow of electricity) a connector is designed to carry, measured in amperes or amps (A). Current ratings on connectors usually range from 1A to 50A.
  • Voltage describes the voltage rating of the connector, measured in volts (V). Typical ratings are 50V, 125V, 250V, and 600V.

Contact Size

Contact size, also referred to as "termination size," is often used to describe the range of wire gauges that can mate with each contact. It could also be represented as the diameter of the contact itself.

In North America, wire size is measured according to the American Wire Gauge (AWG) standard. The higher the AWG number the thinner the wire. This is because AWG stems from a measurement that represented the number of times the wire was run through a wire machine, which reduced the diameter of the wire. Thus 24-gauge wire went through the machine 6 more times than 18-gauge wire.

Number of Contacts

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


CR4 - Circular connector pin terminology

Image credit:

Amphenol Aerospace Corporation


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