> Except for plumbing.. 1" PVC Sch 40 pipe has no dimension that's
> 1". It does have an od that's the same as some iron or lead pipe
> that DOES have a 1" id.
"One inch" pipe does NOT have an ID of 1". It's actually about 1.05"
for schedule 40, less than 1" for schedule 80.
You are correct that both PVC and iron pipe have the same OD, which
is 1.33 inches for "One inch" pipe.
Many years ago (like 150) "one inch" pipe actually had an ID of
one inch and an OD of 1.33 inches, hence a wall of .165 inches.
When schedule 40, 80, etc, was introduced, they standardized on
the 1.33 inch OD so the threads would be the same. The ID then
became a function of the wall thickness. The thickness that are
called out happen to result in the ID being different than the pipe size
except 4 inch schedule 40 which happens to coincidentally have
an ID of 3.999 which you can call 4 inches if you like. I think
the thicknesses in the schedule were chosen for a certain water pressure.
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