| 摘要 |
The frame (1) has two horizontal bearing surfaces (6A, 6B) and two sloping support surfaces (6C, 6D) adapted to co-operate with matching support surfaces (12A, 12B, 12C, 12D) integral with the covering element. The sloping support surfaces (6C, 6D, 12C, 12D) slope downwards towards the horizontal support surfaces (6A, 6B, 12A, 12B) opposite the sloping support surfaces (6C, 6D), and the frame (1) is provided with stop means (8, 9; 14A, 14B) which, when the covering element (2) is subjected to the action of a vertical force applied on some point, co-operate with matching stop means (13; 15A, 15B) integral with the covering element (2) so as to cause the latter to turn about said stop means (8, 9; 14A, 14B) of the frame (1) until it reaches a position of stable equilibrium in which the covering element (2) rests with its four support surfaces (12A, 12B, 12C, 12D) on the corresponding support surfaces (6A, 6B, 6C, 6D) of the frame (1). |
