[sdiy] Knob inserts/clips for D-shaft pots

[MTG]

I have a pile of pots that I would like to use, but they are round 1/4" 
shaft (with perhaps a little bit of spline-ness). These knobs need to work 
with (I think they are called) D-shaft pots of the matching diameter.  I 
have noticed that some knobs have a metal thingy that is inserted so that 
the knob mates with a D-shaft. Does anyone know where to get those, or what 
they are really called? The alternative I guess is to buy some cheap knobs 
with them inside and pull them out of the cheap ones and put them in the 
nice knobs that I want to use.  I figured this list has some serious knob 
wizards if anywhere does.

GB