A leader is any length of line that is closest to the bait and/or fish on the line. There are several purposed for using a leader and the material of the leader varies according to purpose. Metal leaders are typically used when toothy fish are the target or are around and threaten the primary line. Fluorocarbon leaders are used when the target species is “leader shy” and/or spooked by visible line emanating from the lure or bait; fluorocarbon is invisible in water. Commercially available leaders frequently have a swivel at one end and snap at the other. The swivel prevents twists in the line. The snap makes changes to the lure or hook fast and easy.
Snap swivels are just the swivel and the snap and I recommend that you always use one at the end of your primary line. With a snap swivel on your line, you have the option to (1) easily snap the lure directly on, (2) snap a leader on and then the lure, or (3) snap some other tackle in addition to a leader and the lure – for example, a teaser. I typically use a use a fluorocarbon leader and move to metal only when necessary (typically when the bluefish are prevalent). Striped bass are sometimes shy when they see the line coming from the lure – particularly in the case of swimming lures. I find that Stripers aren’t as picky about surface lures – probably because the line is not as evident at the surface with waves, foam and other surface noise. Mini tunas are very shy about presentation and almost require fluorocarbon.
I tie my own fluorocarbon leaders. I tie a 42” length into a long loop and use it doubled. I double it and hide the knot with a piece of shrink-wrap from an electronics store. One end of the loop can be clipped to the snap swivel while the other can loop through and around the lure. This style of leader is not as convenient without the snap but it’s far less visible without the snap.
My favorite teaser is simply a smaller loop made from fluorocarbon that is threaded through a hook. After tying the knot, I slip a commercially available buck-tail teaser over the hook and clip it onto with the leader and lure. To the fish, this looks like the lure is chasing the teaser. There are times when every hook-up is on the teaser and the fish it catches are not always schoolies!