Lexmark 302 - Manual (Page 171)

4. Align the blue slotted opening on the bottom of the ribbon
cartridge with the metal post. You may have to turn the blue
ribbon advance knob to align the slots. Lower the ribbon
cartridge onto the metal post. Be sure that the plastic tab on the
bottom of the ribbon cartridge aligns with the hole in the printer
casting.
B l u e S l o t t e d O p e n i n g
M e t a l P o s t
T a b