| 摘要 |
<p>The device consists of a pair of discs, joined by a hub and held together by a screw with wing nut. Thread is wound round the hub until a ring of the desired width is formed: this is then held together by stitching, the needle passing through a radial slot in each disc. Each disc has several slots diametrically opposed and regularly spaced. The distance pieces from which the hub can be chosen are of various lengths and external profile.</p> |
