Keen

This ability doubles the threat range of weapon. For instance, if it is placed on longsword (which has a normal threat range of 19-20) the keen longsword scores a threat on a 17-20. Only piercing or slashing weapons can be keen. (If you roll this property randomly for an inappropriate weapon, reroll.) This benefit doesn’t stack with any other effect that expands the threat range of a weapon (such as the Improved Critical feat).