Floor vent handle knob - how to remove?

'68 Chevelle, with push/pull floor vents. How do you remove the chrome knob? Don't want to break it, can't find a clip and it doesn't want to unscrew. Am taking off the floor side panels in preparation to paint the car.
thanks for your help.
Tom

I think they are pressed on with ribs on the shaft. You don't have to take them off to remove the kick panels for paint. To remove the kick panels without breakage, pop the grill out with a small screw driver, remove the 5 screws. The knob and cable will still be attached. You might want to remove both sill plates and on the drivers side you need to remove the e-brake. One bolt under the dash and two from firewall engine side. Also be careful of the thin piece that goes under the pads they crack easy. Good luck let me know how it turns out.

Molhannah,
Thanks for the reply - that's good to know that the whole panel can be removed without taking apart the knob. I'll do that for both sides. The sill plates are already off. One step closer toward paint prep.
Tom B.