PURPOSE: To make repairs for a defective tip ever so easy, by insetting a fitting convex part of a tip lower part into each socket being installed in an outer circumferential side end of a disclike blade body at every specified interval in a row, and locking it thereat tight enough.
CONSTITUTION: A void 9 installed in an inward part of a socket 1 is provided with an opening 10 at a side end part in a rotational direction of a blade A, and a partition wall 11 is formed at a side end part in a reverse rotational direction, while an opening groove 12 being narrower in width than breadth of the void 9 is formed in a circumferential direction. On the other hand, a tip 4 has a fitting convex part 6 to be fitted in the socket 1 in its lower part, and the sectional form and length are almost congruent with the void 9 in size whereby any play after its fitting in the socket is well reduced. A triangular concave part 16 is installed in a side wall of the opening groove 12 at the side of the socket 1, while a convex part 17 being almost congruent with form of the concave part 16 is formed in a side wall 13 of the fitting convex part 6 and further an engaging part 15 for preventing it from slipping off is formed therein.
