Abstract: A golf club head includes a half-circle metal ring that extends outwards from the rear surface of the head. The weight of the half-circle metal ring is adjustable according to the weight of the head. The half-circle metal ring can be a solid ring or a hollow tube. By change in diameter of the cross section of the half-circle metal ring, the center of gravity moves back in the club head and the center-of-gravity angle as well as the depth of center-of-gravity are both increased so as to achieve greater hitting efficiency.