The 640 on printsheet was the mainstay of Australian production for 4
decades. Starting with the 1938 Zoologicals, it continued, unaltered to the end of the
Four post office sheets were guillotined from the printsheet, each post
office sheet contained 2 panes of 80 portrait stamps, 10 rows of 8.
Because the interpane gutter was the same size as a stamp (to accommodate the comb
perforator), most issues had one or (mostly) two inscribed lines in the central gutter
between panes as a security precaution.
Until their abandonment, imprints appeared in the lower left
corner of EACH pane of 80.