On Tuesday, 14 March 2017 20:37:59 UTC, James Wilkinson Sword wrote:
On Tue, 14 Mar 2017 19:58:18 -0000, Tim Watts wrote:

On 14/03/17 18:33, James Wilkinson Sword wrote:
On Tue, 14 Mar 2017 18:24:38 -0000, Nightjar wrote:

So the pipe wall was so thick that the inner diameter was 0.5" and the
outer 0.825"? I could understand that with HEP pipe, but not metal.

Iron pipe is pretty thick walled.

To allow for rust?


No, to allow for the threads to be cut into it.
There are three steel pipe wall thicknesses commonly available for different pressures.

http://www.engineeringtoolbox.com/bs...ions-d_97.html

The outside for all gauges is constant.
The bore varies depending on the pressure the pipe is rated for.
This is so all pipes take the same BSP thread when they are threaded.

Hence the bore size quoted is "nominal".