Dumb question, but: These are designed to be attached to a swivel to spin, correct -- not to be fixed to an eye to "flap" (?)

Eric sorry I missed this. Yes use a small split ring, 20lb is plenty big, attach to a swivel. The other end of the swivel can be put on the tail loop before it's closed...saves space.

what types of plugs are the Charktails best suited for?

I bought some and have yet to add them to any of my plugs...

Chris i use some on needles, two belly hook design with the tail off the back, also they work killer on small top water spooks, the tail throws so much water, drives em nuts.

NEEDLESSSSSSSSSSS all the way

Thanks, Salty. I have a couple of waking needles underway I'm going to try your needle-sized charktail on.

I'm sure the "whup-whup-whup" of the tail slapping at the surface can be a great attractor at certain times, but I added extra weight to the tail of these needles to keep the blade under the surface when waking at regular speed...It's amazing how much additional weight was necessary to keep the blade from planing the rear of the plug all the way to the surface. Good news is the additional weight in the rear helped offset the loss in casting distance due to the blade.

I'll post a couple of pics when done.