Nothing really to explain you are correct..
5/4 is the size of the stock (nominal 1 1/4" thick) before it is surfaced
two sides (S2S). to it's actual size.
Your choice is to pay more for S2S where the mill or supplier does surfacing
for you or you pay less for the rough cut wood and do the job yourself.
Third choice is to pay almost twice the price of rough cut stock for ready
to go, sold by the linier foot stuff at a store like Lowes or Home Depot.
Surfacing two sides doesn't and usually isn't the same thing sanded and
ready to have a finish applied. You will almost certainly still have to do a
fair amount of work to get the stock to that point.
The cost of rolling your own from rough cut stock can be hefty in either
price, power tools, jointer and surface planer, to do the job efficiently,
time/work with hand tools, a good hand plane that you know how to use and
take care of, or a combination of both, most start out with the off the
shelf and ready to go stock.
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