shrinking head

from The Collaborative International Dictionary of English v.0.48

Shrinking \Shrink"ing\,
   a. & n. from {Shrink}.
   [1913 Webster]

   {Shrinking head} (Founding), a body of molten metal connected
      with a mold for the purpose of supplying metal to
      compensate for the shrinkage of the casting; -- called
      also {sinking head}, and {riser}.
      [1913 Webster]