Gregg ruling is 1/3″ or 3 spaces to the inch, with a single margin drawn down the center of the page.
If you want to create your own custom Gregg sheets, here are the settings for two sizes (8 1/2″ x 11″ and the steno pad size 6″x 9″). Just plug in these same numbers (though you may want to choose a different line color… I picked lavender).
Without the Vertical Middle Line
With the Vertical Middle Line
Based on Plays_with_Pens custom practice page (this is in portrait mode):