. They are made by Extreme Archery Products.
That's correct.
They're actually called SHRINK FLETCH, which uses a pre-fletched shrinkable tube fletched with duravanes, that would fletch 17/64 & 24/64 arrows in diameter.
All you do is, slide the shrink fletch over the arrow and then sumerge in
'hot water' and the tube tightens to the arrow.
You can also perfectly align the vanes with the blades on a broadhead.