(Sigh) the things I do for this board...
OK, just so I could enter a number and keep you guys happy, and so I could vote and see the results of the poll, I spent a few minutes just now working on my tool, and managed to get it to just on 17cm. That's measured along the top, from the root where it meets the body to the tip, which I believe is the standard means of measurement.
I am pretty sure it would be longer if it were someone else doing the measurement though! It's like quantum physics - the observer affects the measurement.