Most manufacturers will claim a tolerance over a 28 inch span. So for +- .003" in 28 inches a shaft can vary .003" in one direction and .003" in the oposite direction for up to .006" total "crookedness".

I have never measured any of mine so I couldn't tell you first hand which ones are more consistant. From what I have heard the carbon express arrows are suppose to be one of the most consistant.