Patent attributes
The present invention includes a shaft that protrudes further toward a lower spindle side than an upper rim and includes a plurality of engagement grooves arranged in an up-down direction at an outer periphery of a lower end accommodated in a hollow portion of the lower spindle; a shaft support part that rotatably supports an upper end of the shaft; an engagement part that is accommodated within the hollow portion and is engaged with any one engagement groove of the plurality of engagement grooves; a first elevating part that is configured to integrally move the upper spindle, the shaft, and the shaft support part in the up-down direction; and a second elevating part that adjusts the length of the shaft protruding below the upper rim by changing the distance between the shaft support part and the upper spindle.
