a. [ Pref. bi- + filar. ] Two-threaded; involving the use of two threads; as, bifilar suspension; a bifilar balance. [ 1913 Webster ]

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. [ 1913 Webster ]