The STX Original SYNC Series putters offer a variety of head shapes and hosel designs to fit any eye or putting stroke. Some of these putters use STX's bullet back design. These bullet backs have a thinner face and a cylindrical extension jutting off the back. This design puts more mass behind the impact area of the face. The SYNC putters also have two inserts, softer and harder, so a player can choose the feel that they prefer, or adjust to slow or fast course conditions.