| 摘要 |
<p>Balls (4) alternating on either side of the side plates (2 and 3) are housed in holes (1a) provided in the central web (1), bear into spherical cavities (2a or 3a) provided on the internal side of the side plates (2 or 3) and extend on the outside through holes provided in the other side plate (2 or 3).</p> |
