The Little Gem Neck Adjuster
Turning this screw clockwise causes the cam device to press against the hoop, thereby angling the neck to correct for unsuitably high action.
This is the patent for Shattuck's novel invention.
The Little Gem fits inside the neck heel through this recessed cavity:
And here are some photos of the device itself:
Our deepest thanks to our new friend Barry for supplying these photos of the Little Gem in his restored Lansing.