What is the difference between a helical fletch and an off set fletch? Some companies sell arrows made with either 2 or 4 degrees off set fletching, and I' m trying to figure out how that differs from helical.

You might go to Truflite feathers home page their
information has been very helpful to me on my
change over to feathers and what degree to use!

Helical actually rotate around the shaft at a higher rotation usually, where offset are straight to the shaft but at a slight angle.