Gyro Transmitter, AN5751-1, Flux Gate Compass System F8F thru which the bottom stem

thru which the bottom stem would protrude

See photo from the TBM Avenger Pilot Manual dated Nov 1945

This Radio Compass Indicator is labeled for use in the WWII-era Air Corps US Army's C-3 Link Trainer

as used in Bombers Boeing B-17 Flying Fortress and Consolidated B-24 Liberator

or opened and resealed at some point in its journey

Gyro Transmitter, AN5751-1, Flux Gate Compass System F8F thru which the bottom stemThe Gyro Transmitter AN5751 1 was an integral component of the WWII era Bendix Gyro Flux Gate Compass System used in aircraft such as the B 17, B 24, and B 29. The 7 component Flux Gate Compass system was designed to provide accurate navigational guidance using the earth's magnetic forces by minimizing interference from the systems of the aircraft, such as its turrets, guns, and engines. A flux gate gyro transmitter typically located within the wing