Like an auto mechanic's torsion wrench (before the days of air-driven wrenches), this bobbin takes the guesswork out of winding thread, and all but eliminates broken thread at the same time. Each model features a solid brass arm and a click drag adjustment to regulate the thread tension. The small diameter ceramic no-wear tube and removable vinyl grip on the standard model of this fly tying tool allows intricate work with fine thread on the smallest to large hooks. The standard model has a range of 1 to 9 oz. tension and the mag model has a range of 2 to 16 oz.