Abstract: The invention relates to an adjusting device for adjustment of a dimension of an object, applying especially to adjustment of a dimension of an object intended to be worn by a user, such as a helmet. The device comprises a pinion with first teeth, free in rotation about an axis in a housing, and a rack provided with a row of second teeth, slid freely in translation into the housing. The second teeth cooperate with the first teeth so that rotation of the pinion causes translation of the rack. The rack is deformable elastically, such that when a force is exerted on it in the direction opposite the direction of translation during rotation of the pinion, it undergoes elastic deformation.