Hi Mark,
Thanks again for your help. However, in your model you've extruded elements along the length of the parts; I want to revolve them around the axis, so that I can model the end fillets (which you've 'removed') as well as a non-parallel "diameter".
Sometimes I can make this work, and often I can simply select two end surfaces to mesh between which works very well. However, sometimes it refuses to select the second surface and if I pick vertices instead I get the message "Selected references do not form a valid mesh region."
In one case it even allowed me to mesh a volume at one end of the part, yet refused to recognise the identical volume at the other end...
What's causing this error message?