Stonfo Bobtec 1 Adjustable Tension Bobbin - Genius! Stainless steel bobbin with slider to adjust the thread tension. Allows a quick change of the spool. The Stonfo Bobtec 1 Adjustable Tension Bobbin is perfectly balanced when spun; making it spin smoothly when using the split thread method for dubbing loops, or when flattening thread. Hardened steel tube is very smooth preventing thread fraying.