| 摘要 |
<p>There is disclosed a method for introducing a helical formation (11) into a flexible tubular material (12). The material (12) is supported together with a surrounding helical former (13) so as to deform the material (12) to have a helical indentation (11) corresponding to the shape of the former (13). The material (12) is then set in that configuration and the former (13) is removed.</p> |
