25c Transpacific China Clipper top plate block of six
Four plates were used to print this air mail stamp issue. They are 21473, 21474, 21475 and (shown) 21476.
This top margin of a block contains six stamp illustrating Martin M-130. Only three such airplanes as were actually built. They were named the China Clipper, the Hawaiian Clipper and the Philippine Clipper.