I used a spare length of the wishbone tubing that I had kicking about, 33.7 OD
However after a re-read of the IVA manual .... I don't think I have placed it high enough
The question of cross bar tube size was talked about recently .... it would appear that my crossbar is a tad on the light side ( Can't find the thread )
If I have to change the height .... Going to go for some 40mm OD tube with a wall thickness of 3mm .... Seamed or seamless tube, I doubt it will make a great deal of difference