38mm Diameter Control Knob With Aluminium Bezel And Pointer Mark, Suitable for Short Shafts



This type was chosen because the grub screw fixing is quite low down on the shaft and there is a recess in the black plastic on the underside.  This allows the tuning knob to fix onto the fairly short shaft of the variable capacitor, and the recess in the plastic avoids them clashing with the variable capacitor fixing bolts if used.  It is designed for round shaft diameters of up to a true one quarter inch, 0.25" or 6.35mm.  This is handy should you happen to have a scrap 500pF variable capacitor with a 0.25" shaft recovered from an old radio, which would afford a somewhat larger tuning range.

Both 6.0mm and 6.35mm shaft diameter types are available in this style of knob.  Finding out from suppliers which one they are actually selling can be a minor nightmare, usually involving a preliminary test purchase.  After which, they send you the wrong ones from a different bin. 

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