Zebra ZD400 Series field upgradeable serial module. The serial module option does not come preinstalled with any printer. Compatible with the following Zebra Printers: ZD421D, ZD421T, ZD421C, ZD611D, ZD611D-HC, ZD411T, ZD411D, ZD411D-HC. Important: This is not backwards compatible with the ZD410 or TLP Printers.