The shaft straightness measurement tells you how close to perfectly straight the group of crossbow bolts you are purchasing really is. For instance, most crossbow bolt shafts on the market have straightness measurements that range from 0.006” to 0.001”. This means that if your bolts are said to have a shaft straightness of 0.006”, then the arrow shafts will be up to 0.006” from being straight. Granted, 0.006” is very close to being straight, however arrows that have a shaft straightness of 0.001” come much closer to being perfectly straight. Arrows that have a smaller shaft straightness measurement have a likelihood of shooting more accurately and with greater precision than ones that have a larger tolerance, and hence, are more expensive.