The heavy-duty spring in the base swings the arm so that the molten metal is forced into the flask. The broken arm construction assures that the metal will flowing a straight line, producing dense castings. NOTE: For safety reasons, casting machine springs must be replaced at the factory. Takes flasks up to -31/2" in diameter and 5" high. The long 22-3/8" arm provides the extra force needed for heavier casts. Comes with balance weights and cradle for 2-1/2" diameter flasks.