PURPOSE: To bring the axis of the neck portion and the axis of the stem portion in accurate alignment to enable correct sealing, by providing a first and second V-notch portions on one side of a supporting block having the same notch angles and being in alignment with each other, whereby the neck portion and the stem socket are supported by the first and second V-notch portions, respectively, to fit therein, so that the axis of the neck portion and that of the stem portion are kept in accurate alignment and correct sealing is made possible.

CONSTITUTION: The supporting device 21 consists of the lower base plate 22, the supporting block 23, and the upper base plate 24. The supporting block 23 comprises the neck portion supporting block 25 and the stem socket supporting block 26, both the supporting blocks 25, 26 being made integral through the connecting block 27, and the same is fixedly disposed on the top surface of the lower base plate 22. On one side 25a, 26a of the supporting blocks 25, 26, there are provided V-notches 28, 29 having the same notch angles and being in alignment with each other. By this arrangement, the axis of the neck portion and that of the stem can be kept in accurate alignment to enable correct sealing.