| 摘要 |
<p>Projecting portions are formed at portions on circumferential edge portions of a pressure plate 2a which are brought into abutment with locking pieces 20, 21, and circumferential end edge portions of the locking pieces 20, 21 are caused to float from the circumferential edge portions of the pressure plate 2a. Thus, circumferential end edges of the locking pieces 20, 21 which constitute sharp ends are prevented from being brought into strong frictional contact with the circumferential edge portions of the pressure plate 2a.</p> |
