quadrant-plate

from The Century Dictionary.

• noun A metal plate at the end of a screw-cutting lathe head-stock, which carries a stud on which one or more gears may be placed to connect the lead-screw to the spindle. The plate is hinged on the lead-screw and the stud for the intermediate gears is in a slot so that gears of almost any desired diameter can be used, thus making possible a great many changes in the speed of the lead-screw and providing for the cutting of different threads on the work.