| 摘要 |
PROBLEM TO BE SOLVED: To improve the duralibity of an enlarged blade. SOLUTION: A plurality of radially rotatable enlarged blades 23 are pivotally supported to the tip of this device. The tip of the enlarged blade 23 is provided with a wide part 26 wider than the base end side, and wide groove parts 28 with which the lateral sides of the wide part 26 are engaged are formed at fitting grooves 21. Excavating efficicney is improved by widening the tips of the enlarged blades 23, and durability is improved since the tip side wide parts 26 are engaged with the wide groove parts 28.
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