You are looking at #C46 Hawaii Air Mail FDC on ArtCraft cachet with plate block, very rare.  The total FDCs in Scotts Catalogue is approximately 90,000.  With one plate block being available on each 50 pane sheet, there is a potential for 1,800 FDCs with plate block.  This is extremely low quantity that makes this lot a must buy.  This is a nice item available at auction.