Ditto what Arthur P asked. I shoot Muzzy 100 gr. 3 blades with a 4" right helical vane through my whisker buiscuit and have outstanding arrow performance. If you shoot mechanicals you can go with 4" straight, but if you shoot fixed, go helical. Length IMO would be dictated by size of broadhead (ie: diameter and weight) If you have a large cutting diameter (1.5 or up)you might consider the 5".