As already stated. Valve adjuster. I had 3 of them and sold 2 on eBay got about 50 bucks each.
Thats actually top dollar, good job. Did they have the knob in the above photo, or was it a round knob (no bumps) with knurling, and a hex drive around the center flat driver?
The 1920's ones had the round knob, and used special hex drive sockets, and the 30's ones used a larger hex drive, and then the 40's and 50's ones used a 1/2" square drive.
There is also a T handled one that was made for Pratt and Whitney.
Mostly on GM 6 cylinders.
They go back way before that!
