No, definitely .4". 2 pins will fit equally spaced between the two
rows, and if you mentally swing 4 pins 90 degrees, you can visualize the
width.
Hang on, if you get 2 pins between the 2 rows, that's 0.3" spacing :
o o o o
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4 pins, 3 gaps, each gap is 0.1", so 0.3" total. I've soldered enough
0.3" IC sockets onto stripboard to know you get 2 columns of holes
between the columns of pins, too...
-tony