I use them for skwerls and bunnies, sure. They were discussed during talks about building CHEAP small game arrows. Essentially taper the front as normal and screw on a 3/8" nut, hence the name. I tend to coat the area with super glue before and after adding the nut.
Others find that using a wingnut increases their hitting power. Whatever.
I find that they knock the wits out of a skwerl, but may not kill it. I pick the critter up, hold it against the tree and whack it with my Shrew hawk. game over next.
I also like the nutters cause I really don't fear shooting them up in the air (trees) and wondering who I might be hurting when they land.
ChuckC