Allen wrote:
Softwood --  shrinks, often unpredictably in width -- sometimes as much as
3/8" to 1/2" on a box from the time it is freshly cut, and not always uniformly
over the length of a board.  Even using dried wood -- which good box makers
do -- it is hard to guess what the final shrinkage will be in advance.

Comment:
This is the word from a beekeeper with many years of experience. I
can't emphasize too much how valuable this is. I learned this same
thing many years ago -- from another experienced beekeeper.

PS. In bee equipment, never make the bee space too small,  this is
much worse than too big.
--
PB