An accessory for a golf putter to make that putter into a putter with the feel of a belly putter. As the rotary member is suspended on a first stationary member and rotatably supported on a second stationary member spaced apart from the first stationary member, components can be easily centered and assembled with structural stability. The invisible machine readable code may not absorb or reflect visible light substantially differently from the printable surface, in one embodiment. An end of a signal terminal of the flexible circuit board is electrically connected to a signal electrode of the optical modulating device. % based on the total amount of the dry composition. Mounted on the shaft is a hub having an engagement finger for controlling gear engagement devices, which is configured to oscillate in the space between two fingers of a selection mask, which is mounted on the shaft axially movable therewith and is guided with respect to the casing so as not to follow rotation of the shaft and the hub when a gear is engaged.