mobow, Gregs right, right spin keeps the points tight, the head spins right(clockwise) to screw into the arrow, if you hold the head, the arrow is spun right(clockwise) to tighten the head.

However, Offset will do the same as helical and a straight clamp with the ability to either fletch straight or offset is more versatile than a helical clamp. If you go with a Bitz, which I too feel is the best on the market, go with a straight clamp and offset as hard as your rest and arrow allows you.