Patent ID: 8579326

Claim:
An extensible support leg comprising at least two reciprocally-slidable portions ( 20 , 21 ), a maneuvering screw ( 5 ) axially constrained to a first portion ( 20 ) of the portions ( 20 , 21 ), a threaded volute ( 4 ) axially constrained to a second portion ( 21 ) of the portions ( 20 , 21 ) and screwed on the maneuvering screw ( 5 ), and a rotating drive shaft ( 8 ) which is connected to the maneuvering screw ( 5 ) by means of a mechanical gear change ( 70 , 71 , 80 , 81 , 86 ), and is destined to be rotated in order to set the maneuvering screw ( 5 ) in rotation, the mechanical gear change ( 70 , 71 , 80 , 81 , 86 ) further comprises: two first cogged crown wheels ( 70 , 71 ), coaxial and rotatably solid with the maneuvering screw ( 5 ); two second cogged crown wheels ( 80 , 81 ) mounted coaxially and rotatably idle on the drive shaft ( 8 ), each of which enmeshes directly with a respective cogged crown wheel of the first cogged crown wheels ( 70 , 71 ), such as to realize two gears having different transmission ratios, and a cursor ( 86 ), which is rotatably solidly associated to a portion of the drive shaft ( 8 ) comprised between the second cogged crown wheels ( 80 , 81 ), and is mobile, in a direction of the axis of the drive shaft ( 8 ), between a first enmeshed position and a second enmeshed position, in which the drive shaft ( 8 ) is rotatably solid respectively with one of the second cogged crown wheels ( 80 ) and with the other ( 81 ).