Bifilar

a.
  1. Two-threaded; involving the use of two threads; as, bifilar suspension; a bifilar balance.
    2. Bifilar micrometer (often called a bifilar ),
    an instrument form measuring minute distances or angles by means of two very minute threads (usually spider lines), one of which, at least, is movable; -- more commonly called a filar micrometer.