"Circular connectors" are cylindrical, threaded multipin connectors also called "socket" connectors. Among their main characteristics there is the capacity to offer a decidedly firm and safe connection, precisely by virtue of the possibility of screwing - in the true sense of the word - the male connector with the female one. This system can be used to convey many signals and, in most cases, the internal part precedes the use of pins of conductive material which ensure electrical contact.
The Audio Effetti catalog has a huge assortment of circular connectors so that you can always build customized wiring.