The X Size box contains the printer command which sets the rectangle width.
For the Diconix 150 Plus printer, the X Size box is empty.
For the HP LaserJet IIP printer, the Horizontal Rectangle Size command (ESC*cnA) specifies the rectangle's width in 1/300 inch units. The argument n specifies the number of units.
To specify the Horizontal Rectangle Size command, type the following in the X Size box:
\x1B*c%dA