PROBLEM TO BE SOLVED: To minimize the mass and inertial moment as much as possible by providing a corresponding fixed part for arranging a corresponding fixing element in an empty part, and making it possible to lay the corresponding fixing part into a fixed and engaged state with the fixing part of a fixing bolt element. ;SOLUTION: A toothed ring 16 has a hollowly formed disc entrained tooth 24 and a vertically extending empty part 44. The through-port 54 of the empty part 44 has the larger opening cross section on the end part separated from the end area 68 of the toothed ring 16, and a fixing stone 70 for fixing a lid 18 is fitted to this surface. The fixing stone 70 has a corresponding fixing part 72 contact parts 74, 76 extended in the exactly opposite direction thereto, and the profiles thereof correspond to the forms of the through-holes 54, 50 closer to the end area 68. When the male screw part 92 of a screw 90 is screwed to the female screw opening part of the hole 86 of the corresponding fixing part 72, the fixing stone 70 is moved axially toward the end part 68 until a stopper is formed. The lid can be thus fixed to the toothed ring with a short fixing screw, and the weight can be reduced by use of the above components.;COPYRIGHT: (C)2000,JPO
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