I believe the normal helical (twist as you call it) is about 3 degrees. This helical is what imparts a rotation on the arrow for better broadhead flight. This helical is recommended for feathers or vanes. If you look closely at the newer style vanes (Blazers, NAP Twisters and Quik Spin XTs and others) you will notice that one side is smooth while the other is ridged or winged to cause air drag on that side which causes arrow rotation. These should be applied either straight or with no more than a 1 degree helical.