| 摘要 |
<p>The frame has a central circular opening with three 120 degree spaced housings in its internal edge, to take the peripheral tenons (5) of a removable circular groove. The housings have an engaging ramp (10) and a locking counter slope (25) inclined towards the base. The interior face (12) of each tenon has a lug (13), sliding on the ramp and bearing on the counter slope. The lug is spherical and has, from the interior face of the tenon, a cylindrical shape, ending hemispherically, and extending upwards by a spherical mitre on the side facing the counterslope.</p> |
