Drop The Hammer
In recent years, the size and diameter of swivels and line (especially braid) has become smaller and smaller. Now it's to the point where I'm having trouble getting purchase on the swivels to tighten knots adequately, and I'm sure that I'm not the only angler in this boat. My solution is to use a claw hammer as a "third hand." Insert the swivel into the gap between the hammer claws, with the line on the outside of the claws. The claw of the hammer has a tapered gap, which allows almost any size swivel to be inserted. The beveled edge of the claw's gap also provides a solid seat for the swivel body as you pull the knot tight. This arrangement works for almost any size swivel, light to heavy, and provides a mechanical advantage that makes knot tying a breeze.
Havelock, North Carolina