Abstract: An electric hair clipper includes a hair thinning comb attachment detachable to a housing provided with a cutter assembly. The comb attachment is formed with a row of hair guiding slots which is in parallel and juxtaposed relation with the cutting edge of the cutter assembly for guiding the hair past the cutting edge in the process of hair thinning operation. A rotary adjustor dial is mounted on the housing and is drivingly connected to the comb attachment for varying the relative position of the comb attachment to the housing and therefore the distance between the row of the hair guiding slots and the cutting edge, thus adjusting the cutting length of hair intended by simple manipulation of the rotary adjustor dial.