The original stamps overprinted as air mail unit postage stamps are those of $7,000 denomination of Dr. Sun Yat-sen issue of the second Shanghai Dah Tung Print. The characters〝國內航空郵資已付〞(domestic air mail postage paid) in No. 5 Regular Writing characters appear in two vertical lines in black, between which the character〝陝〞(Shen-abbreviation for Shensi Province) was overprinted in brackets at the bottom.