| 摘要 |
PROBLEM TO BE SOLVED: To reduce a load applied to a fork arranged in an axial center part and to improve the strength reliability of a blade implanted part. SOLUTION: Grooves are positioned on a radially peripheral side sequentially from an axial end part to an axial center part, and the positions of the grooves excluding the grooves 7a, 7h in the axial most end part have a shape projected toward a radial periphery. Thereby, a part of loads applied to a fork 5d positioned in the axial center part is shared to forks positioned on an axial outer side therefrom.
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