Danville Monofilament Fly Tying Thread- .006- Danville is one of the oldest fly-tying thread companies the U.S. In reference to thread size and strengths, they are used as a standard. Danville Mono Thread is a .006 diameter monofilament thread used for ribbing flies and various other applications. Breaking strength is around 36 ounces. 100 yard spools in clear.