Abstract: The device of the invention consists in a telescopic element with two arms, one of them movable within the other, having in its corresponding ends attachment means (3), so that the shorter arm (2) has means with an axial groove (5) which in the normal working situation is operatively opposite in respect to an axial chamber (6) of the internal portion of the longer arm (1), so that in said chamber a blocking element is movable vertically in respect to the groove, preferably a cylinder (7) opposing the effort of an elastic element located within the corresponding housing (11) which is encased in said groove (5) blocking the device and permitting its unblocking once the effort of the elastic means on the cylinder is exceeded. The device is reusable and it is easily adjustable to different levels of effort for its unblocking.