1) Having or using two filaments 2) Having two threads 
having two threads
• (a.) Two-threaded; involving the use of two threads; as, bifilar suspension; a bifilar balance.
Two-threaded; involving the use of two threads; as, bifilar suspension; a bifilar balance. 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. ... Source: Websters ...
Bi·fi'lar adjective [ Prefix bi- + filar .] Two-threaded; involving the use of two threads; as, bifilar suspension; a bifilar balance. Bifilar micrometer (often called a bifilar ), 
[adj] - having or using two filaments
adjective having or using two filaments; `a bifilar suspension of a waving part of an instrument`
furnished or fitted with two filaments or threads.