Abstract: A coupling comprising a first member defining a socket, a second number such as a tube defining a spigot inserted into an open end of the socket, and a locking device received within an annular gap defined between an inner wall of the socket and an outer wall of the spigot. The locking device comprises circumferentially spaced load-bearing members, each load-bearing member extending within the annular gap from a first end which is relatively close to the open end of the socket and a second end which is relatively remote from the open end of the socket. Each load-bearing member is resiliently biased such that the first end engages the socket and the second end engages the spigot, and each load-bearing member is dimensioned such that it acts substantially as a beam in compression to resist withdrawal of the spigot from the socket.