IBM 3270 Option Instructions page 13

14.
Align the slot in the adapter card retaining bracket with
the hole in the rear of the unit. Start the screw clockwise;
then tighten it with a flat-blade screwdriver or a 3/16-inch
nutdriver.
[3 [ 3 [ 3
~~--------------~------------~I
Not
Aligned
Properly
Aligned
AP A Adapter 9