Here is a block consisting of three columns of US Sc.#266 type II at left and two columns of Sc.#267 type III at right.
Brookman devoted two pages to this interesting juxtaposition of types. There were some 125 million of the type II issued and nearly 7.5 billion of the type III. 207 plates of 400 subjects each were used in printing the type III, but on one plate, #170, the types were mixed on the upper right pane. The other three panes of plate #170 were all type III. So there were ten combination pairs from each run of plate #170.
Such combination pairs of 266 and 267 were sought after, but not often found of course among the billion plus of such stamps out in the wild. By now many, if not most, blocks have been broken down for sale in pairs. This particular block is a favorite of mine, but it's very delicate so I try not to jostle it when turning album pages as some perfs are separating.
First the block, then a higher res close-up to contradistinguish the type II and type III triangles at positions 3/4 and 8/9 of this block.
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