the jaw in order to press the countermould against the inner face of the bar the means for ejecting the countermoulds rapidly when they are removed during the opening of the gripper result from the combined effects of the disengagement of the jaw from the notches and from the expansion of the compression springs acting on the studs stops which has the consequence of driving the studs downwards the invention will be better understood by means of the following detailed description given with respect to the accompanying drawings illustrating an embodiment of the invention provided by way of example fig1 and 3 are a partial front view a view in cross section along line ii and a plan view of a cross section along line iii of an extraction gripper with the countermoulds fig4 and 6 are a partial front view a view in cross section along line v and a plan view in cross section along line vi of a variant of an extraction gripper with the countermoulds fig9 shows in cross section a gripper with a variant of the countermould studs fig1 11 12 and 13 show in cross section means for guiding the main moulds and countermoulds on the return run of the chain fig1 16 17 18 and 19 show in cross section the sequences of extraction and replacing of the countermoulds in fig1 to 3 an.