Spinner Knobs - shaft sizes and undersides?

[Afterburner]

I have been contemplating adding a spinner to my cab for a long time, but by golly I'm going to do it!

I've told my wife I want a SpinTrak for Xmas if I haven't built my own spinner by that time.  I'm hoping a deadline to save $70+ will help spur me along.

I have spent all afternoon fiddling around with various take-out parts I found around my shop and just haven't been happy with anything I found.  I tried a couple of hard drive bearings, and even found a sturdy bearing/shaft from a small fan.  But each of those had their shortcomings.

I went back on the net to look at some write-ups and look at some current spinners (like SpinTrak) and wow they have evolved.  I really liked the way the SpinTrak and TurboTwist seem to have become nice sealed units with a footprint not much bigger than a standard arcade button.

That got me thinking and I rummaged around and found an old button with a dead microswitch.  I gutted it and kept the threaded outside so I can use the usual plastic nuts to mount it to my CP.  I was looking at some ball bearings and am likely going with a couple that are 7/8" OD and accept a 1/4" shaft.  That appears it will fit (nearly) perfect inside the button housing.

As I will likely just purchase a knob I was wondering what size shaft they accept?  Is it 1/4"?

And if I end up with a standard plastic button nut on top of my CP, are the knobs hollow on the underside with all the mass at the outside  and a shaft receptacle at the center?  Or are the knobs solid?  I may have to draw something up quickly to make my question clearer.