| 摘要 |
<p>To facilitate restriction of a top ratio, a stopper plate 24 is mounted on the open end of an annular wall 31 provided at the outer circumference of a movable face 21. When the movable face 21 is moved toward a fixed face 20, stopper slant surfaces 35 of the stopper plate 24 overlap guide slant surfaces 34 of a ramp plate 22 to thereby stop further movement of the movable face 21, thus restricting the top ratio. <IMAGE></p> |
