Oki C3520 - Manual (Page 96)

Maintenance > 96
8. Lower the new belt unit into place, with the lifting bar at
the front and the drive gear towards the rear of the
printer. Locate the drive gear into the gear inside the
printer by the rear left corner of the unit, and lower the
belt unit flat inside the printer.
9. Turn the two fasteners (a) 90° to the right until they lock.
This will secure the belt unit in place.
a
a