Where did the term "China Rails" come from

The thread stated wrong or right welcome. My interpretation of the china rail is the extension of what is referred to for years as the china wall. China rails were just the extension added to the top of what is referred to as the china wall.

Wherever you bought a W5 top end the question that came up was, Were the China wall intake extensions included?
Roger that Sir. Key word for me is “Extensions.”
Extensions that go on top of the China wall.
No matter, we’re all good here.