leveling-screw

from The Century Dictionary.

• noun In a mill, a screw in the hurst or frame on which a run of millstones is placed, used to give a vertical adjustment and bring it to an exact level. It acts against an iron plate set in a bedstone.
• noun In a surveying or portable astronomical instrument, any one of the screws used for leveling the horizontal plate or that part of the instrument on which the horizontal angles are read off.