Abstract: An adaptor for converting to a push-to-connect tube fitting/port a standard tube fitting/port body having a threaded portion for threaded attachment of a nut/plug, comprises a coupling nut/plug having an axially inner threaded end portion for threaded attachment to the threaded portion of the fitting/port body; a tube sealing member contained within the nut/plug for sealing to a tube having a locking surface spaced from the end of the tube; and a retention device retained in the nut/plug, which nut/plug has at an axially outer end thereof a central opening through which the tube can be inserted into the coupling nut/plug, whereby the locking surface can be engaged by the retention device to prevent axial withdrawal of the tube from the coupling nut/plug once inserted; wherein sealing and retention of the tube is effected within the confines of the coupling nut/plug and separate from and without requiring modification of the standard tube fitting/port body.