Tone Adjuster
Gibson's infamous
Here's a peculiar item from one of Gibson's "dark periods." In the late 60s, when they were making some less than spectacular guitars, they came up with this bright idea.
In case your J-200 got to be too loud and resonant, you could screw a big steel mass upward to press against the top and keep it from vibrating too much:
It's hard to imagine that this clunky thing is an original "feature." No wonder we called some of these J-200s "whispering giants!"