15mm Shower pipe problem - Fitting shower head!

[Gopher]

Hi All

I need some advive on shower heads, basically in my bathroom I have a pipe fed through the celing and fixed (the pipe is 15mm).

Now I am looking to buy a square showerhead like this one:

(Please go to the bookstore, click through on any book and put this in the search box - Bristan-Square-6-Shower )

However there are no details of size or possible fittings. I have seen showerheads which have like a 'ball fitting' so they can be adjusted.

What I want to know is: Is there a standard size for these? Has anyone done this and knows what to buy and where?

Thanks in advance.