These machined bobbins have a hardened steel tip insert and countersunk feed that allows the thread to glide through the tube for super-smooth threading and tying. The ADJUSTABLE DISC-DRAG has an extensive adjustment zone so that you can FINE TUNE THREAD TENSION to the type of thread being used, and your personal preferences. Bobbins are very lightweight and feel great in your hand while tying. Saltwater model has a larger diameter tube for use with heavier threads.