Kevin is right. The larger sizes are used as by guys fishing for giant tuna between the main line and flouro leader since they pass thru the roller guides they typically use easier. I've had guys bring the smaller sizes on the boat for bottom (...)
I use SPRO barrel swivels for pike , stripers/blues with 40 lb fluro about 30" or so. That being said, I would never send a metal swivel through the guides. My go to for freshwater is 30 lb braid tied direct to 15 lb fluoro. Choose your knot.
