Source : Webster's Revised Unabridged Dictionary (1913)

Doublethreaded \Dou"ble*thread`ed\, a.
   1. Consisting of two threads twisted together; using two
      threads.

   2. (Mech.) Having two screw threads instead of one; -- said
      of a screw in which the pitch is equal to twice the
      distance between the centers of adjacent threads.