Your box of fly fishing tackle is bound to contain swivels. As you fish, the bait often causes your line to twist, and a swivel will stop that happening. Mind you, some baits don't twist as much as others, so a swivel may not be necessary for those. When shopping for swivels, look for quality ones than spin easily. While a barrel swivel can be made very simply and are cheap, the higher-quality ones have a ball bearing in them and turn with very little pressure. The latter are usually stronger than the barrel swivel, too. Use them when fishing for hard-fighting fish, trolling, or for any type of fishing in which the bait spins a lot.
A black or dark swivel is a good idea when you fish for species that like to attack shiny objects. A swivel is also useful for stopping the lead and keeping it away from the bait. For a certain type of bass fishing, for example you thread a Bullet Weight on your main line and tie a swivel to it, then attach a leader from a few inches to several feet long. This keeps the bait away from the lead. It can also be used for live bait as well as plastic worms.
Conventional swivels have a loop at each end to attach line to, but you can also get three-way swivels with three loops for the line. These work well for bait walker rigs and any other time you need to tie more than one leader to a swivel. Frequently, they are not as a normal swivel, so make sure you've got a quality three-way swivel in your fly fishing tackle box if you’re going after big fish.
