We use methods of physicochemical hydrodynamics to study the working principles of a thermophoretic microgear in which an axially symmetric temperature gradient causes rotational movement of a heated rotor in the shape of a pinion confined in a cylindrical cavity filled with liquid. Calculations indicate that the rotation of the microgear arises from differences in the physicochemical properties along the edges of the teeth. The angular velocity of the gear under load decreases linearly with the load torque. The resulting characteristics of the thermophoretic gear are compared with that of a thermoosmotic engine having comparable parameters. Optimal geometrical parameters of both systems are discussed. It is shown that performance of the two devices is similar.