"Volume attenuator for 100 V line loudspeakers. Maximum regulated power of 40 W. Safety functions for announcements by line switching and speech preference. Six levels of regulation by means of a 12-position endless switch, with a ""zero"" sandwiched between each two levels. 45 mm key, compatible with Optimus M-420x trim frames (not included) and electrical series (see models). Universal box mounting (included)."