Post Office Seal, 1948, gray black, hyphen-hole perf 9½, Experimental Booklet Panes. Group of 3 items comprising OX38 booklet panes of five with the "16-56146-1 GPO" imprint, one on soft gray paper (one of six recorded) and one on thick cream paper (the only recorded example), both o.g., lightly hinged, a March 4, 1942 cover bearing bottom seal from a pane of five on thick cream paper, tied on back by "Opened in Dead Letter Branch, Des Moines, Iowa", the only recorded use of these seals (date is consistent with the use of the type 10-14 seals and predates the issue of 1949 by seven years), Very Fine, a unique and important exhibition group, all illustrated and discussed in Kotanchik (proof.164). Scott No. OX38 var.  Estimate $750 - 1,000. The post office began to experiment with the use of hyphen hole perforating and booklet formats in vertical pane of five seals, as early as 1942, demonstrated by the cover offered here. The experimental panes are characterized by the inscription in the top selvage that reads "16-56146-1 GPO" rather than "16-56164 GPO" that was used for the 1949 and 1968 issues. $0 (Image)