Installs on the top of the printer. This unit supports up to 550 sheets of paper (20 lb, 75 gsm). Up to 3 output expanders may be supported at a time. Envelopes, transparencies, card stock & label are also supported with this option. When both an output expander & high capacity output stacker are installed, the output expander must be installed above the high capacity output stacker. The output expander supports bin near full & full sensing.