A deflector for a mechanical reduction gear of a turbine engine, for example of an aircraft, is configured to be inserted between two adjacent planets of the reduction gear. The deflector includes a block having a first lateral surface that is cylindrical and concave and has a radius of curvature R1 measured from an axis G1. The block also has a second lateral surface, opposite the first lateral surface, that is cylindrical and concave and that has a radius of curvature R1 measured from an axis G2 that is parallel to G1. Each of the first and second surfaces has at least one protruding tab having a generally elongate shape about the respective axis G1, G2 of the surface considered and having an internal periphery that is concavely curved and a has radius of curvature R2 measured from the respective axis G1, G2, R2 being less than R1.