Link 1 is connected by screw pair A to the fixed link and by screw pair B to link 2. Link 2 has key a which slides along keyway b of the fixed link. Adjusting link 1 has external and internal threads of the same hand and with a slight difference in pitch. When link 1 is turned one revolution, link 2, prevented from turning by key a, is displaced a distance equal to the difference in the pitches of the external and internal threads.
$2252$LS,PS$