Lexmark 4I3 - Manual (Page 197)

6. Align the holes in the ribbon guide with the ribbon guide posts on
the print head carrier. Press the guide all the way down on
the ribbon guide posts until the tops of the posts are even
with the top of the ribbon guide.
R ib b o n G u id e
R ib b o n
G u id e P o sts
Chapter 4. Replacing Your Ribbon 4-7