Circular connector contacts are the components of a circular connector that carry the electrical signals across a connection. They are typically attached to each wire strand within the cable with a solderless crimp mechanism, using a crimping tool. Each circular connector contact is then passed through the connector housing and the circular connector insert before the connector backshell is closed to provide strain relief.
Circular connector contacts are usually available in matched male and female versions for a particular connector standard. Typical contact materials are brass, steel or gold-plated, and which you choose will depend on the connector standard you're working with or whether you need low contact resistance in high signal integrity applications.
The modular nature of circular connector contacts means individual contacts can be replaced without necessarily needing to replace the whole connector. The contact material can provide protection from environmental contamination, for example by preventing corrosion from moisture in the air in marine environments.