Hornet
posted this
17 February 2023
I thought that looked familiar. I did some digging and found one that I inherited from my dad. Unfortunately, it is missing the same part/parts. From the looks of it, I would guess that it had a 0.281 diameter pin about 1-1/8" long with a flat on it with a "flag" attached to the flat to contact the end of the L-handled screw to stop the inward travel on the actual groove roller and control groove depth. There may have been another flat on the portion of the shaft that goes into the hole that would register with the end of the thumb screw to orient the flag to the offset of the groove rolling wheel to the center of the pin.The 1974 Herter's Catalog doesn't show any details either. I'd like to see a picture if you can find one or make one that works...
Looks like the distance from the base to the grooves is adjusted with the large knurled screw with the locknut on it.