since you know you are selecting just those two verts and not more at a time, you can up the # as much as you want. By doing one set at a time, you can use .01-.1 or even more to get it to work, but it could cause problems if you select more than one set of vert's. .0001 usually works when you are sure that the verts are right on top of each other. THanks,
Brian