Characteristics of electrical connector and its pinout, and physical construction, size, contact resistance, insulation between the pins, durability and vibration resistant, resistant to ingress of water or other contaminants, pressure resistance, reliability, lifetime (number of disconnected operation until a failure occurs) and ease of connection and disconnection. They may be key, you can prevent the insertion direction errors, wrong pins connected to each other, and lock mechanism, to ensure that they are fully plugged in and cannot work loose or falling out.

Some connector design, prior to when you insert some pins to others, contact and break the first time disconnects; this protection is usually in the connector of the power circuit ground correctly, hot-swap applications such as connection security first, and sequencing connections. Usually best to connectors are easy to visually identify, quickly assembled, requires only simple tools, and cheap. In some cases, the device manufacturer may choose a connector, in particular because it is not compatible with those from other sources, what possible connection admission control. There is no single connector has all the properties of the ideal; the proliferation of types reflects the different requirements.

Keyed many connectors are keyed, and some mechanical components, this prevents mating except for the correct matching connectors. This can be used to prevent incorrect or damaging interconnections, are not compromised is stuck or prevent the pins at the wrong angle or fitting has not yet fully-fit plug, or prevent damaging connections, plug the audio cable into a power outlet. For example, XLR connectors have a notch to ensure proper orientation, while micro-DIN plugs have a plastic projection, which fit perfectly into the outlet hole and prevent different connectors that squeeze together (they also have a notched metal skirt, provide secondary keying).