Abstract: An electro-fusion fitting (10) includes a body (12) of thermoplastics e.g. polyethylene, with a heater element (14) connected to heater terminals (16, 18) and identification devices (60, 62) moulded in the body (12). The devices are connected to the heater terminals and to identification terminals (20, 22). A control unit (24) connects a reference voltage (74) in turn to the device (60) and then to the device (62). In each case the device forms a voltage divider with a resistance (80) so that the value of the device is found. The two values identify the fitting so that the time the element (14) is energized can be set automatically by the unit (24) for each different size or kind of fitting. Neither device is required to be a specially accurate component and the range of values of the devices is less than it would be for a given range of fittings if only one device was used per fitting.