A cylindrical elongate body having proximal and distal ends and enclosing two similar longitudinally extending lumens separated by a septum and a further lumen within the septum. The frame may be injection molded or cast, and may include sculpted, variable cross section eyeglass components. The unit may comprise multiple multi-threshold units operatively coupled to the dither volume, and each multi-threshold unit may be used to dither a separate component of a contone color pixel. Finally, a pulse modulated signal as either a function of the bandlimited exponential signal or the coefficient vector is generated. The metal anti-shift collar may be a zinc alloy, an aluminum alloy, or a magnesium alloy, for example.