[Hallicrafters] B-42 SX-42 base.

[Waldo Magnuson]

"Actually the knob and screw are the -easiest- parts to build if you have 
-any- kind of metal lathe.  Even a little Unimat.  And building yourself 
you can make them really good looking ie.  stainless steel and brass all 
shined up, and knurled , fluted, and contoured.  73  Gary"

Hi Gary,
   I don't think many people know the knob / screw is a double-extension screw.  I made one out of aluminum with only a single extension and even then it took about an hour.  I'll take and post some pictures of mine.  Unless you look closely and know what to look for, it is hard to tell from an original.
73,  Skip  W7WGM