| 摘要 |
<p>Four sides fit parallel to each other with a clearance on swivel pins. Second (2) and third (3) sides fit on a first side (1) so as to swivel on a first (S1) and second (S2) swivel pins respectively. A fourth side (4) swivels on a third swivel pin (S3) vertical to the first or second swivel pins.</p> |
