double-headed rail

from The Collaborative International Dictionary of English v.0.48

Double-headed \Dou"ble-head"ed\, a.
   Having two heads; bicipital.
   [1913 Webster]

   {Double-headed rail} (Railroad), a rail whose flanges are
      duplicates, so that when one is worn the other may be
      turned uppermost.
      [1913 Webster]