| 摘要 |
<p>A plastics sheath is moduled round the screw, an external sheath round the plastics sheath locating it positively in the axial direction, and forming with it a concentric expansion absorption chamber. The external sheath is in two parts (5a, 5b) fitted together round the plastic one (2). The parts can be of metal, and the plastics sheat can have a portion forming a plug for the external sheath. Both sheaths can engage together so that they cannot turn in relation to each other.</p> |
