This was removed from my model 3000 brake lathe, it installs in the hole on the power panel for storage.  On the model 3000, there is a switch inside that this tool activates which allows the machine to operate normally, but when the tool is removed, the spindle motor does not run.  I don't know exactly how, but this grinding wheel dresser attached to the spindle or drum somehow and allowed the operator to dress the grinding wheel for the drum brake grinder attachment.  It's in good condition, I'm not sure if it was ever used.  This was removed from machine serial number 10202.  Mid 1950s I believe.