UTC Ultra Thread 280 Denier - Ultra Thread has been engineered as a fly tying thread from the beginning. It is not an "off the shelf" thread as are many others. All of Ultra Thread's characteristics were carefully chosen to enhance its tying performance. This is a great size for heavy hair work, attaching dumbbell eyes, large saltwater patterns, and anytime that a large, strong, thread is needed. Ultra 280 has a breaking strength of approximately 4 pounds and is recommended for sizes 6/0 - 2 flies. Large, strong threadApprox. 4 pound breaking strengthRecommended for size 6/0 - 2 flies