Walter Cohen wrote:
My patio overhang has two posts that bear some of the roof weight and,
from what I can tell, these look to be constructed of probably an iron
pipe enclosed squarely by two lengths of 5 1/4" wide board on two sides
and two lengths of 3 3/4 " wide board on the opposite sides (making a
box around the pole.

The lower portion of the 3 3/4" wide boards is rotting due to its
contact (and water) with the patio blue stone. I want to cut out about
2 feet of both planks of this width board and replace it with new board
(and prime and paint). Unfortunately, this is an odd sized board
width. Typical board widths (lets say a 1x4x6 board) has the width of 3
1/2", not 3 3/4". I have no idea where to obtain such a width board.
What am I missing here? Did the original builder/carpenter cut down
vertically (length-wise) a larger width board to make this odd sized 3
3/4" board?

Now what?

As marson says, you'll have to either cut down a 1x6 or use ply
(possible if the edges are hidden).

As a note, if the house is older, it's likely the material was nominal
1x4 and simply was a little wider than today's material.

The other alternative is that if it is 20-years or older, much finish
material did run wider then and for a visible trim piece the builder
used architectural trim stock, not just run-of-the-mill construction
lumber (it was still affordable back then).

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