Clarification - the knob I’m looking for was used on Western Electric-made WW2-era “RU” receivers and “GF” transmitters when fitted for local control.

Enclosed is a picture and text copied from Henry Rogers RU/GF webpage - https://www.radioblvd.com/RU16-GF11_Restoration.htm

2. Direct Coupler - MC-127 - For “local” operation of the receiver tuning there was a small direct coupler tuning adapter that could be installed in lieu of the Receiver Tuning Head. Where installation called the radio op to have the receiver in front of him, the MC-127 coupler eliminated the flex drive cable and remote tuning head…. The MC-127 greatly reduced the backlash that was inherent in the flex drive cable operation. However, the minuscule size of the MC-127 hampers easy fast tuning with the crank and most tuning is done slowly by using the “fingers on the wheel-rim perimeter” approach...