[sdiy] Source for dual Concentric shaft pots?

[Louis van Dompselaar]

These work on the same principle:
http://www.dompselaar.org/concentric.jpg (from a mixer I'm currently 
scavenging for parts)

As far as I can tell, they're also just two regular knobs with the cap 
missing from
the bottom one.

As an aside, does anyone know what kind of tool to use on the screws 
that are
inside these knobs?

> Rean collet knobs (like the ones I've used for my JH-720) are made to work 
> with concentric pots: the collets of the bigger knobs have a hole for a 
> smaller shaft to go thru. Then you don't need a cap for the knob: A smaller 
> knob, which is mounted on the thinner shaft, sits where the cap of the 
> bigger knob would have been. (I never built something with concentric pots, 
> but I held two different sized of these knobs together, and it's amazing how 
> it fits.)
>
> Here you see some larger Rean knobs without cap - easy to imagine how the 
> samller ones would fit on top of them:
> http://jhaible.heim.at/tonline_stuff/jh_720_in_progress_1.jpg
>
> I guess th esame thing works for "classic" collet knobs like Elma.
>
> JH.