Abstract: A device to control and protect the operating mechanisms of vertical slats for window blinds, contained in a box (1) in which there is a pinion consisting of outer (4) and inner (3) members. The outer member (4) has a partial set of vertical gear teeth and is limited in its rotation at the bottom end of the box. The inner member (3) supports the slat and goes through the outer member, extending above into an orifice (14) in the cover (9) of box (1). It is provided with a projection (3') that limits its rotation inside cover (9) by interacting with projection (23). The two members of the pinion are connected at the top by a tab that corresponds to a notch. The cover 9 can have play with reference to a flexible intermediate wall (24) inside the box.