| 摘要 |
<p>This invention relates to a plastic pipe having in its wall punched holes 16a, b, c; 16 min a, b, c, with rounded short end edges 2a and long continuously curved side edges 15 and to a punching knife for making the punched holes, having a large length/width ratio in cross-section with curved side flanks 6 between rounded portions 7 and sharp knife edges 10.</p> |
