A brand and type (like Crescent wrench) of multi pin connector used in audio systems and equipment for connecting multi pair cable with one connector (instead of many). Elco is made in the U.S. and Edac is made in Canada and both come in many different varieties. They both come in 20, 38, 56, 90, and 120 pin configurations. There are male and female connectors (plug and receptacle in Edac nomenclature). The male connector can be identified by its polarizing pins on the plug, whereas the female has polarizing sockets. Either sex can have the actuating screw or the fixed nut for attachment. All that is required is that there is one each. On the back of an ADAT, for example, the Elco is a female 56 pin, with fixed nut. The cable you plug in, therefore, is a 56 pin male with actuator screw.