Abstract: The socket of a plug and socket type coupling is mounted with an assembly tool which makes sure that a threaded connection between the socket and a mounting member is properly tightened. When the socket is to be mounted, the socket is operated to a disengaged condition and the assembly tool is inserted into the socket. The socket is then operated to an engaged condition. This causes locking elements in the socket to engage the assembly tool to hold the assembly tool in the socket. Torque is then applied to the assembly tool. When the threaded connection has been tightened to a desired extent, a breakway section of the assembly tool fractures to interrupt the transmission of force to the socket. The socket is then operated to the released condition and the end portion of the broken assembly tool is removed from the socket. A plug is then inserted in the socket to enable fluid under pressure to be conducted through the coupling.

Abstract: Amplitude modulation systems for underwater communication have a number of disadvantages. For example, with a number of divers attempting to communicate simultaneously, intolerable cross-talk occurs. Variable tuning is necessary to overcome this problem. However, the invention disclosed herein uses angle modulation (phase or frequency modulation) which inherently has fewer noise problems and, because of the "capture effect" reduces any cross-talk problems. In an exemplary embodiment an audio transducer feeds a modulator to produce frequency modulated radio frequency signals which are fed to a balanced modulator together with a fixed frequency radio frequency signal from a local oscillator. The output of the balanced modulator comprises ultrasonic frequency signals which are frequency modulated in accordance with the audio signals. Also disclosed is a receiver for such ultrasonic frequency signals.