A mechanical reduction gear is suitable for a turbomachine and, in particular, a turbomachine of an aircraft. The reduction gear includes a sun gear, a ring gear formed by two half-ring gears, planet gears arranged between the sun gear and the ring gear, and at least one shaft rotationally fixed to the ring gear. The reduction gear further includes an annular covering part that extends around the ring gear and is independently fixed by flanges and/or splines to each of the half-ring gears.