Control Unit C-4, of ARN-7 Automatic Radio Compass, for Parts or Repair F7F Tigercat see illustration from its Erection

see illustration from its Erection and Maintenance manual dated 1945

This is a Course Selector

On the back is a lock/free screw

operates in the same manner but has greater air volume capacity for larger aircraft with more air-driven instruments such as a heavy bomber or transport

Here are 6 spare Gyro Caging Knob Mechanisms for the Artificial Gyro Horizon

Control Unit C-4, of ARN-7 Automatic Radio Compass, for Parts or Repair F7F Tigercat see illustration from its ErectionHere is a WWII era Control Unit for the ARN 7 Automatic Radio Compass system used for direction finding and homing. The receiver function tunes from 100 1750 kHz across 4 bands, which were selected by rotating the center knob below the frequency band window. The center knob rotates a flexible shaft connected to a rotatable loop antenna. The ARN 7 system (see diagram), were one of several generations of radio navigational systems installed in an