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Originally Posted by ratdog
Plumbing pipe diameters are inside dimension.
No, they are not. Pipe (NPT) dimensions are "nominal" and, in smaller sizes, not even close to the actual diameter, either inside or outside.
The actual outside diameter of several pipe sizes, and the corresponding inside diameter of schedule 40 pipe, all in inches, are:
1/8" NPT; OD = .405, ID = .265
1/4" NPT; OD= .540, ID = .360
1/2" NPT; OD = .840, ID = .618
3/4" NPT; OD = 1.050, ID = .740
1" NPT OD= 1.315; ID = 1.043
Schedule 40 is most common in metal pipe while a lot of PVC is Schedule 80 which has thicker walls and, therefore, a smaller ID. The OD's remain the same for all nominal sizes in all materials.
BTW, PVC pipe is available in 3' lengths at any hardware store or home center in various standard diameters at very low cost. All you need is a hacksaw.