Measurement of steel pipe

[woodman-46]

Hello,
I am in the process of buying some threaded steel pipe from ebay. The 3/4" pipe is advertised as 26.9mm of( outside dimension) but surely should be 19.05 mm.I thought this might be a mistake but their other measurement seem to not tally as well and other sellers have the same thing. What am I missing here?
Thanks
James

 

[RandomGrinch]

The measurement relates to the bore diameter.
It's useful, because pipes may have different wall thicknesses - the outside diameter will vary, but you still want a 3/4" pipe!

 

[JohnD]

British Standard Pipe measurements are not the same as what they are called.

A half inch fitting measures nearer 3/4"

Because it fits on the outside of a steel pipe that is quite near to half an inch internal diameter.

3/4" is more than an inch

Even half inch pipe is not actually 1/2" i.d.

You can look up a table of dimensions on Wiki or goggle.

Metric pipes, however, are called after their External diameter

So 15mm metric measures 15mm and is nearly the same as 1/2" imperial, and fits the same

 

[woodman-46]

I really appreciate your speedy advice and responses.
Thanks and Happy Christmas