In order to install ribbon for ZEBRA GX420T, follow these steps:

• Remove the wrapping and pull pull its adhesive strip free.
• Open the printer and place the new ribbon roll.
• Rotate the roll until the notches are aligned and lock into the left side of the roll core.
• Install the Take-Up core.
• Rotate the roll until the notches are aligned and lock into the left side of the roll core.
• Pull the transfer ribbon's leader off the roll and attach it with the adhesive strip on the leader to the empty ribbon core on the Take-Up spindle.
• Rotate the thumb wheel on the left side of the supply spindle until the ribbon is pulled tight across the print-head.