There are a number of caveats with pipe sizing. In addition to the concept of schedule there is also a 'Standard' (STD) weight which for the most part is schedule 40 up to 12". Larger STD sizes have a constant wall thickness of 0.375". There is an 'Extra Strong' (XS) which is usually schedule 80 up to about 8" before it changes. There is also an "Double Extra Strong' (XXS) which usually has a thicker wall than schedule 160 up to about 8". And dogdays is right, up to 10", Schedule 40 ID is the nominal ID of the pipe. 12" is an oddball. 14" and above the OD of the pipe is nominal size.

Can you tell I do this for a living?


"We live in a time when intelligent people are being silenced so that stupid people won't be offended".