The Collaborative International Dictionary of English v.0.48:

Swage \Swage\, n.
   A tool, variously shaped or grooved on the end or face, used
   by blacksmiths and other workers in metals, for shaping their
   work, whether sheet metal or forging, by holding the swage
   upon the work, or the work upon the swage, and striking with
   a sledge.
   [1913 Webster]

   Swage block, a perforated block of iron, having grooved
      sides and adapted for use in heading bolts and swaging
      objects of large size.
      [1913 Webster]

WordNet (r) 3.0 (2006):

swage block
    n 1: an iron block cut with holes and grooves to assist in cold
         working metal