A connector (10) has a male part (12) connected to a female part (50), and each has a passageway which is coaxial with the other when the parts (12 and 50) are connected. A collet (24) surrounds the male part (12), is coupled thereto, and has an external screwthread which engages an internal screwthread on the female part (50), whereby relative rotation between those screwthreads in a given sense causes the female part (50) to sealingly engage the male part (12). The collet (24) has a slot (40) extending longitudinally with respect to the axis of the screwthreads to enable it to be splayed. A wedge (34) between the male part (12) and the collet (24) is displaceable longitudinally with respect to the axis of the screwthreads to splay the collet (24) and lock the male and female parts (12 and 50) together in a sealing engagement.