To prevent a handle from being dislocated even if a fitting member is inverted by forming the radii of the inner faces of engaged projections so as to be slightly larger than the radii of insertion parts and fitting parts of a fastening tool and forming small projections for dislocation prevention between the insertion parts and the fastening parts.

The fastening tool 25 is provided with an engaged hole 26 which is slightly larger than a diamond engaged part 20 and which is engaged with slight allowance, an abutting part 27 to/on which a disk-like flange part 21 is polymerized and abutted, the plural insertion parts 28 into which the engaged projections 8 of the fitting member 5 inserted, the fastening parts 34 where the engaged projections 8 which are inserted deep into the insertion parts laterally move for every fitting member 5 and the engaged guide bodies 29 of a taper, to which the upper faces of the engaged projections 8 are engaged when the fastening parts 34 are laterally moved. The radius r1 of the inner face of the engaged projection 8 is formed so as to be lightly larger than the radii r2 of the parts of the insertion parts 28 and the fastening parts 34 in the fastening tool 25. The small projections for dislocation prevention 35 are formed between the insertion parts 28 and the fastening parts 34. The small projections for dislocation prevention 35 gradually become high on the side of the insertion parts 28.