Datamax ST-3210 Operator's Manual page 22

"Print Side Media Sensor" using Roll Stock –
Mount the roll of ticket stock on the Roll Hanger so that it
unwinds in the direction shown by the arrow in the drawing
below. (The TOF Marks must be wound outward on the roll; see
Section 6 for ticket stock specifications).
Ensure that the Printhead Latch is in the 'Locked' position.
Roll Hanger
Loosen the Thumbscrew and adjust the Media Guides to fit the width
of the ticket stock.
The guides should be positioned so that there is no side-to-side ticket
movement (too loose), but not so close as to cause friction or bowing
of the ticket (too tight); see the illustration below for examples.
Once properly positioned, tighten the Thumbscrew to secure the
Media Guides in place.
14
Unlocked
Locked
S-Class