Our volunteers came across several adjustable ceramic coils in boxes with part numbers. We did not remember seeing these in instruments.

These coils are unique and use external snap rings in grooves in the ceramic for the solder points. That is most both unique and unusual.

A quick look in the Replaceable Parts Registry (RPR) identified them as used in the 190 Constant Amplitude Signal Generator which was introduced in 1954. A quick look on TekWiki provided internal photographs showing seven of these adjustable ceramic coils.