Thanks again Cat - have a good afternoon at work. An update for anyone who's interested - I've managed to find my measuring jug (Cat was right about the other tumblers also holding 10oz) and these Whitefriars hi-balls at 5.25in/13cm tall are definitely the M33 10oz ones that go with the M33 2pt water jug. Anything taller than that I would suggest are probably the M34 12oz tumblers.