An electrical connector has first and second matable connector housings with circular cross-sections, and has a fixing ring which is rotatably mounted at an outer circumference of the first connector housing. In use, the fixing ring is engaged with the second connector housing to form a screw-action cam mechanism. This draws the connector housings into mating engagement when the fixing ring is rotated in a first rotational direction relative to the connector housings. The connector also has (i) a detent for detaining the fixing ring at a predetermined position corresponding to full mating engagement of the connector housings, and (ii) a return spring which applies a return bias to the fixing ring in the opposing rotational direction as the fixing ring is rotated in the first rotational direction.