Thanks, it's as I thought.
I have them in the dashboard but there are 3 more dials to go back in and, of course, I'm still trying to get the glove box liner correct. More V. V. careful sanding away of paint and fiddling with fabric to be done, so it'll be a while before the dash is back in the car. I have this 'itch' that I would like to get them apart, just in case, and it's a darn sight easier now! Anything I tried to grip the top with, that wouldn't mangle up the aluminium, simply wouldn't hold. Was the collet you refer to made to fit the knurled edges?
Happy Christmas everyone.