A device of a roller assembly or a trolley for a cable transportation system, the device comprising: a frame having two facing walls, which are provided with two respective first holes having a first axis in common; a pin that engages the first holes; a body mounted rotatably about the pin between the two facing walls of the frame, the body having a hole, which has a second axis and enables the passage of the pin; and an auxiliary constraining device that is selectively releasable configured to keep the axes of the first holes of the frame and of the hole of the body coincident even in the absence of the pin.